Biomechanics of Human Movement

There are three basic types of spin:

(1) Top Spin; (2) Bottom Spin; and (3) Side Spin-Diagonal Spin. Each type of spin is used differently is sport to maximize performance.

Forces Influencing Projectiles

1. Gravity: minus air resistance path taken is shape of a parabola. 2. Aerodynamic Forces: alters path trajectory

Three factors determine vertical height:

1. Height of the Center of Gravity at Takeoff. 2. Vertical Velocity of the Body's Center of Gravity at Takeoff. 3. Center of Gravity to Fingertip Height.

Goals for Projectiles: 1. Maximize range -- Give examples 2. Maximize total distance-- Give examples 3. Optimize range and flight time-- Give examples 4. Maximize height -- Give examples 5. Optimize height and range -- Give examples 6. Minimize flight time -- Give examples 7. Accuracy -- Give examples 8. What are the ideal projection angles for each??

1. Maximize range -- (shot put, long jump) Shot put optimum angle is approximately 42°(varies by height of athlete and velocity of shot at release Long jump theoretical optimum is approximately 43°; however, due to human limits, the actual angle for elite jumpers is approximately 20°-22° 2. Maximize total distance-- (golf) Because the total distance (flight plus roll) is most important, trajectory angles are lower than 45°lDistance is controlled by the pitch of the club Driver ~ 10° 3. Optimize range and flight time (punt) -- Maximum range occurs with 45°trajectory Higher trajectory increases hang time with minimal sacrifice in distance Lower trajectory usually results in longer punt returns Less time for the kicking team to get downfield to cover the punt returner 4. Maximize height -- (vertical jump) Maximize height of COG at takeoff Maximize vertical velocity by exerting maximum vertical force against the ground. Rearrange COG at height of the jump. 5. Optimize height and range -- (high jump) Basic goal is to clear the maximum height Horizontal velocity is necessary to carry jumper over bar into pit Taller jumpers have a great advantage 6. Minimize flight time -- (baseball throw) Baseball players use low trajectories (close to horizontal) Outfielders often throw the ball on one bounce with minimal loss of velocity 7. Accuracy -- (basketball shot) angle of entry 8. What are the ideal projection angles for each 45° The optimum projection angle is close to 45° because the projection velocity of the ball is almost the same at all projection angles

Gravity

A force of attraction between objects that is due to their masses.

What is a lever? What are the three types of levers found in mechanics? Give examples for each.

A lever is a simple machine consisting of a rigid object rotating around an axis or on an axis. In an athlete's body, bones, joints, and muscles work together as lever systems. The three types of levers are A, R and F levers. Lever A is the first-class lever which is positioned between the resistance and the force. An example of this type of lever is an athlete using a leg press machine or any type of weight training machine. With the leg press machine, the athlete is applying force with their legs on one side of the axis and the weight stack as the resistance applies its own force on the other. Lever R is the second-class lever which is positioned between the axis and the force. The second-class lever is characterized by the force and resistance being on the same side of the axis. An example of a second-class lever is when an athlete performs a bench press on a weight machine. Lever F is the third-class lever which is positioned between the axis and the resistance. An example for this type of lever is a bicep curl.

Mass

A measure of how much matter is in an object

weight

A measure of the force of gravity on an object

Force

A push or pull exerted on an object

What is torque and what factors impact on the amount of torque applied to a system?

A torque is a force applied to a point on an object about the axis of rotation. The size of a torque depends on (1) the size of the force applied and (2) its perpendicular distance from the axis of rotation (which depends both on the direction of the force plus its physical distance from the axis of rotation).

Spin and The Magnus Effect

Aerodynamic lift force can also be created on objects projected with spin-- called "The Magnus effect (force)". Spin creates high and low pressure zones similar to that created by shape.

LIFT FORCE CREATED BY SHAPE

Air flow past an airfoil (wing- shaped object) flows faster over upper curved surface than underneath it. Relationship between flow velocity and pressure is an inverse one, and is expressed in "Bernoulli's Principle." Greater flow velocity, creates low pressure, and vice versa. Air flow moves from high to low pressure zones.

Horizontal Projections for which Takeoff and Landing Heights Are Unequal

An optimal angle exists for each height and velocity of release. 2. Greater the difference between the takeoff and landing heights--lower optimum angle. 3. Greater release velocity--greater optimum angle.

LIFT FORCE CREATED BY ITS ORIENTATION IN SPACE

Angle of Attack The difference in flow velocity (and pressure) may be achieved also by tilting the object relative to the flow of air past it. This is referred to as the "Angle of Attack."

Resolution of the Velocity Vector:

Any given velocity may be resolved into two perpendicular components.

WHAT FACTORS IMPACT ON DRAG

Area of the object facing air flow—Profile Drag • Velocity ofairfloww past the object is too fast for the air to follow the contour of the object's trailing side. • Backfloww" occurs at the surface of the object, causing a large, turbulent low-pressure zone behind object • Frictional forces and Coefficient of Drag (CD), which is an index of how, "streamlined" an object is. • Velocity of moving object-- Based on changing air-flow dynamics-- Referred to as the "Reynolds Number" (or 'Effect"). • For coaching, it is important to realize that the "CD" can vary with body build, orientation of body to air flow, and speed.

KINEMATICS SELF-EXPERIMENT #3: Place two pennies (or nickels) on the edge of a table top. Simultaneously, drop one penny off the table so that it falls straight down while you push the other penny forward off of the table. Which penny will strike the floor first? Try it several times to see. What is the initial vertical velocity of each penny? What force is pulling the pennies down? Does that fact that one penny has a horizontal velocity affect the force of gravity acting on that penny and thus affect the vertical acceleration of that penny?

Both pennies strike the floor at the same time. The initial velocity is zero because they are starting at rest. The force of gravity is pulling the pennies down to the ground. Since both pennies have the same initial velocity and the same force pulling them down in the vertical direction, it would make sense that they would both hit the ground at the same time. Even though one penny has a horizontal motion, the rate at which each penny would hit the ground is Soley based on vertical motion, so the horizontal motion has no effect.

What are centripetal and centrifugal forces?

Centripetal force is needed by the player to maintain his grip. If the rotational momentum is more, the centrifugal force could cause the player to lose his grip and the bat may go of the hand. These forces act when a runner takes a sharp bend leans inward to obtain the necessary centripetal force an apparent force that acts outward on a body moving around a center, arising from the body's inertia. In the case of discus throwing for example, the force that acts as the centripetal force is that exerted by the hand of the thrower onto the discus.

Acceleration

Change in velocity divided by the time it takes for the change to occur

What do we mean by conservation of Angular momentum? How is this concept used in slowing down or speeding up rotational velocity? What role does gravity play with angular momentum? Give examples. What is angular impulse?

Conservation of angular momentum is a physical property of a spinning system such that its spin remains constant unless it is acted upon by an external torque; put another way, the speed of rotation is constant as long as net torque is zero There is no direct relationship of angular momentum and gravity. Gravity is simply an attractive force which pulls an object towards itself. Angular momentum is a result of torque being applied to an object. Torque is a couple force acting on the object which produces twisting moment and helps to rotate the object the product of a torque and its time of duration being equal to the change in angular momentum of a body free to rotate compare impulse sense

ANGULAR KINEMATICS SELF-EXPERIMENT #1: Let's look at the forearm and elbow. Place your forearm on the desk or table in front of you. Now flex at the elbow and lift your hand off the table. Move it toward your shoulder as far as you can while keeping your elbow on the desktop, as shown in the figure below. Did all of the parts of the arm undergo the same angular displacement? Which part moved farther, your hand (point A in figure) or the point of attachment of your biceps muscle (point B in figure)?

Did all of the parts of the arm undergo the same angular displacement? Which part moved farther, your hand (point A in figure) or the point of attachment of your biceps muscle (point B in figure)? No not all parts of the arm undergo the same displacement. Point A your hand goes through the most displacement because it is further from the plane. Point B has the undergoes the least amount of displacement from this figure.

FRICTION SELF-EXPERIMENT #3: Let's investigate another aspect of friction. Does surface area of contact affect friction? Take a hardcover book and lay it on the table or desk (it's important that you use a hardcover book). Push the book back and forth across the table and get a feeling for how large the dynamic and static friction forces are. Try to exert only horizontal forces on the book. Now try the same thing with the book on its ends and sides. Use a rubber band to hold the book closed, but don't let the rubber band touch the table as you're sliding the book (see figure). Are there any noticeable differences between the frictional forces you feel with the book in its different orientations? Try it with another hardcover book.

Does surface area of contact affect friction? Yes, surface area of contact affects friction. The larger the surface area the more friction. Are there any noticeable differences between the frictional forces you feel with the book in its different orientations? Yes, when the book is laying flat, with more surface area, the more friction is created. When the book is standing on its end, it has a lower surface area, and les friction is being created and it is easier to move.

M" is based both on the applied force and the time over which the force is applied--called "Impulse" How can we increase impulse? Give an example from your self-experiment. Give examples from sport

Fill several balloons with water so that each one is about the size of a softball. Take these outside to an empty field or empty parking lot and see how far you can throw one without having it break in your hand. If you exert too large a force against the balloon, it will break. To throw the balloon far, you must maximize the duration of force application during the throw, while limiting the size of the force you exert against the balloon so that it doesn't break. Don't constrain your technique to what you perceive as normal throwing styles. Remember, the best technique will be the one in which you accelerate the balloon for the longest possible time while applying the greatest (but non-balloon-breaking) force. examples of sports, any throwing sports

What happens to the angular velocity and displacement of points on a rotating segment? Are they the same or different? Refer to your self-experiment for an example--Can you give one in sports???

For an object rotating about an axis, every point on the object has the same angular velocity. But points farther from the axis of rotation move at a different tangential velocity than points closer to the axis of rotation

Law #3 (Action-Reaction)

For every action there is an equal and opposite reaction Newton's third law explains how many sports injuries are caused. The more force you use to a hit a tennis ball, the more reaction force your arm receives from the racket. Every time your feet hit the ground when you are running, the ground hits your feet with an equal and opposite force Law of action-reaction: When an object or athlete exerts a force on a second object, the latter exerts a reaction force on the first that is both equal and opposite in direction. The law of action and reaction applies irrespective of whether the items applying force to each other are athletes or inanimate objects.

Define force and motion. What are the differences between linear and angular motion?

Force: any influence that tends to change the state of motion of an object or its dimensions. Motion: is the action or process of moving or being moved. Linear motions describe a situation in which movement occurs in a straight line. Angular motions are movements around the axis. The main difference between these two motions is the direction in which they go, and the movements involved.

What is friction? How might frictional forces impact on athletic performance?

Friction: is a force that acts in opposition to the movement of one surface on another. Frictional forces act against the movement of one surface over another. Frictional forces impact athletic performance because in sports the higher the friction the more avoidance of slipping and permits one to grip the surface better. With better friction and grip it allows the athlete or object to have faster movements. In the case of excessive friction, overload is produced, and injuries may occur.

How might the concept of frictional forces be applied to athletics?

Frictional forces act against the movement of one surface over another, such as tennis shoes on a grass court. Friction is the force that prevents the player from slipping and sliding. When air passes over a surface a frictional force called air resistance is produced, this is particularly important at high speed

Relationship between angular and linear velocities: The greater the angular velocity or the greater the radius of rotation or both, the greater the point's linear velocity

From the knowledge of circular motion, we can say that the magnitude of the linear velocity of a particle traveling in a circle relates to the angular velocity of the particle ω by the relation υ/ω= r, where r denotes the radius. At any instant, the relation v/ r = ω applies to every particle that has a rigid body.

Explain the Kinematics of Projectile Motion-- Galileo's Experiments

Galileo observed that a heavy object and a light object will fall to the ground simultaneously from a particular height. All bodies of any mass will fall down simultaneously at the same time from a particular height. That is the acceleration of all free-falling bodies are same.

What is gravity? What is center of gravity? How do they both affect athletic performance?

Gravity is the force of attraction that moves or tends to move objects with mass toward the center of a celestial body such as the earth or the moon. All objects that have matter have mass and exert a gravitational attraction. The more mass an object has the greater the attraction is. The center of gravity is a point at which the mass and weight of an object or athlete are balanced in all directions. These two both affect athletic performance their weight impacts their center of gravity and their athletic performance. The lower the athletes center of gravity increases the athletes balance and stability. Certain athletes and sports need certain center of gravities to have high performance. The lower the center of gravity the better athletic performance can be, but in some cases of swimming it can vary.

Horizontal Projections for which Takeoff and Landing Heights are Equal

Greatest distance is achieved with a projection angle of 42-to-45- degrees.

What is meant by the saying "if one has an advantage mechanical advantage in force, one will have a mechanical disadvantage in range of motion and speed of movement?

If the fulcrum is closer to the load, then relatively low effort will result in larger, more powerful movements at the resistance end; there will be mechanical advantage. Mechanical disadvantage is when the resistance arm is greater than the force arm

2. What is impulse? What is the relationship between linear momentum and linear impulse? How might you use this concept to slow down an objecting having a large amount of momentum?

Impulse is the product of the force being applied times the time over which that force is being applied. The relationship between linear momentum and linear impulse is that they are equivalent to each other. This means that they will give you the same value. You might use this concept to slow down an objecting having a large amount of momentum by rebounding. This is when the object has time and momentum to disperse energy and force to lighten impact.

Define linear momentum--How is an object's momentum related to its inertia?

Impulse is the product of the force being applied times the time over which that force is being applied. The relationship between linear momentum and linear impulse is that they are equivalent to each other. This means that they will give you the same value. You might use this concept to slow down an objecting having a large amount of momentum by rebounding. This is when the object has time and momentum to disperse energy and force to lighten impact.

CONCEPTS OF ANGLE OF ATTACK

Increases in lift force will occur with an angle of attack, but only up to a critical maximum angle. Beyond maximal angle, lift force decreases and drag force increases due to turbulence. This critical angle, approximately 45- degrees for the discus, is called the "stall angle."

IMPACT OF BODY MASS ON DRAG

Increasing or decreasing object's mass has no effect on magnitude of drag force acting against it. The object's mass does determine, in part, how the motion of the object will be affected by the drag force. CONSIDER A PING-PONG BALL AND A GOLF BALL (OR ANOTHER PING-PONG BALL FILLED WITH WATER)-- OBJECT WITH LESSER MASS WILL BE RETARDED MORE THAN THE OBJECT WITH GREATER MASS. Explained by Newton's law of Acceleration- Acceleration (or deceleration) of an object is inversely related to its mass.)

How is body mass and weight related to both inertia and momentum?

Inertia is the property of mass that resists change. Therefore, it is safe to say that as the mass of an object increases so does its inertia. Weight is the measurement of resting inertia and momentum is the measure of inertia at a certain velocity.

Aerodynamics

Influenced by 2 Main Factors: Drag Skin friction Profile &an object's "streamlined" structure. Lift Shape Angle of Attack Spin

Causes of motion---Define Newton's three laws of motion.

Law of Inertia- all athletes and objects have mass and therefore have inertia. Their inertia is expressed by a desire to remain at rest. If a force is applied against them to get them moving, their inertia gives them the desire to travel at the same velocity in a straight line. B. Law of acceleration: The acceleration of objects or athletes is proportional to the force that acts on them and is inversely proportional to their mass. A more massive athlete accelerates less than an athlete with less mass when the same force is applied to both. C. Law of action-reaction: When an object or athlete exerts a force on a second object, the latter exerts a reaction force on the first that is both equal and opposite in direction. The law of action and reaction applies irrespective of whether the items applying force to each other are athletes or inanimate objects.

Third class lever

Lever F is the third-class lever which is positioned between the axis and the resistance. An example for this type of lever is a bicep curl.

What are the differences between linear and angular motion?

Linear motion is translation from one position to another while angular motion is rotation about an axis or center of rotation. Linear motion can also be viewed as motion of a point and have two types: rectilinear (straight path) and curvilinear (curved path).

How is body mass and weight related to both?

Mass is the measure of the amount of matter in a body. Mass is denoted using m or M. Weight is the measure of the amount of force acting on a mass due to the acceleration due to gravity

optimum projection conditions

Maximize the speed of projection Maximize release height Optimum angle of projection Release height = 0, then angle = 450 Increase release height, then decrease angle Decrease release height, then increase angle

What is momentum? What is inertia? How is body weight related to both?

Momentum is the quantity of motion. The mass of an object multiplied by its velocity. An increase in the mass or the velocity of an athlete increases the athlete's momentum. Inertia is the tendency of an object or athlete to either stay at rest or to move continuously in a straight line at a uniform velocity. Inertia is directly related to mass as a more massive athlete or object has greater inertia than one with less mass. Body weight is related to these two because someone who has a higher body weight will have a harder time going against their momentum and inertia to change speeds and directions.

To understand rotational inertia one must consider two factors (when putting these two factors we come up with how one can increase or decrease rotational inertia--our third factor):

Rotational inertia depends both on an object's mass and how the mass is distributed relative to the axis of rotation Bringing two adjustable masses near the axis of rotation decreases the rotational inertia of the system and therefore, according to the Rotational Form of Newton's Second Law of Motion, the angular acceleration of the demonstrator will increase

What distinguishes velocity from speed?

Speed is the time rate at which an object is moving along a path, while velocity is the rate and direction of an object's movement. Put another way, speed is a scalar value, while velocity is a vector

Define speed, velocity, and acceleration.

Speed: is an athlete's or an objects movement per unit of time without any consideration given to direction. Velocity: is the speed of an athlete or object in a given direction. Velocity can change when direction changes even though speed may remain constant. Acceleration: is the rate of change of velocity. An athlete can accelerate, decelerate, or have zero acceleration. The athlete can be either motionless or moving at a uniform rate.

After angular velocity (momentum) is achieved, the body continues to rotate after removal of the external force.

The body loses or gains angular momentum upon receiving another external force.

ANGULAR KINEMATICS SELF-EXPERIMENT #4: Try the following experiments: Take a book and throw it up in the air so that it turns one revolution about an axis perpendicular to its cover (see figure A below). Now find a heavier book (or a lighter one) and do the same trick. Which book was easier to flip? Which book has less angular inertia?

The book that is heavier book was easier to toss because it has less weight acting on the forces preventing it to rotate. The lighter book has less angular inertia while the heavier book had more allowing it to rotate easier.

What is the difference between the coefficient of static and dynamic friction force?

The coefficient of static friction depends on the nature of materials that are in contact. The coefficient of dynamic friction depends on the nature of the material and the temperature of the material. Value of Static Friction can be zero. Value of Kinetic Friction can never be zero

Speed

The distance an object travels per unit of time

KINEMATICS SELF-EXPERIMENT #5: Let's look at an example that has more to do with human movement in sports and consider what force you must exert against a 10-lb dumbbell to lift it. What are the external forces acting on the dumbbell. When does the lift feel most difficult? When does it feel easier? At what points are you accelerating the dumbbell? Decelerating the dumbbell? When is it moving at a constant velocity? When the dumbbell is held overhead, it is no longer moving, so what is the net force at this point in the movement?

The external forces that are acting on the dumbbell are the force of gravity and the force of you lifting it. When lifting the dumbbell, it feels more difficult to lift up than down and the point where it is most difficult is around the mid-point where your bicep for example, is experiencing the most tension on the muscle. It feels easier when the dumbbell is going down, when gravity is working with it. You are accelerating the dumbbell when you are lifting it up and you are decelerating when you are putting it down. The object is moving at a constant velocity when it is fully lifted and fully lowered because the net force is equal to zero meaning the velocity is constant. The net force at this point in the movement is zero because it is not moving.

ANGULAR KINEMATICS SELF-EXPERIMENT #5: Try these experiments. Take a book and flip it so that it rotates about an axis perpendicular to the front and back covers of the book, as you did earlier (see figure A). Now hold the book so that the covers are parallel to the floor and flip it about an axis parallel to the spine of the book, as shown in figure B. Did it take the same effort to flip the book in both cases? Which spins faster? In the human body about which axis is it easier to rotate? More difficult?

The first flip of the book was easier flip. The rotation that flips faster is figure A. In the human body the axis that is easier to rotate is the longitudinal axis because it is a twisting motion while the others require more of a flip motion. The most difficult rotation is the frontal plane because it is a full flip motion where the object fully has to flip upside down.

Potential energy of height

The greater height something is positioned, the more potential energy it will have a pendulum bob swinging to and from above the tabletop has a potential energy that can be measured based on its height above the tabletop. By measuring the mass of the bob and the height of the bob above the tabletop, the potential energy of the bob can be determined.

What is momentum?

The product of an object's mass and velocity

What is the relationship between torque and angular (rotational) movement?

The relationship between torque and angular movement is the impact of inertia on both. Inertia causes the torque which is a form of an angular movement. They are both angular movements and are proportional to each other.

1. Relationship of force and mass to acceleration:

The relationship of force and mass to acceleration is directly related. The acceleration of an object depends on the force and the mass of the object. Acceleration is directly proportional to net external force applied to the system and inversely proportional to body's mass (inertia). These are all interrelated in the regards of newtons second law of acceleration.

KINEMATICS SELF-EXPERIMENT #6: Take a ball in your throwing hand and see how far (or how fast) you can throw it using only wrist motions. Move only your hand, and keep your forearm, upper arm, and the rest of your body still. This is not a very effective technique, is it? Now try thrown the ball again, only this time use your elbow and wrist. Move only your hand and forearm and keep your upper arm and the rest of your body still. This technique is better, but it still isn't very effective. Try it a third time, using your wrist, elbow, and shoulder. Move only your hand, forearm, and upper arm, and keep the rest of your body still. This technique is an improvement over the previous one, but you could do even better. Try it a fourth time, throwing as you normally would with no constraints. This throw was probably the fastest. In which throw were you able to exert a force against the ball for the longest time? For the shortest time?

The shortest time would be the first movement because you have less time with the ball because the movement is a quicker movement with less range of motion. The movement with the longest time is the last movement with a normal throw because you are exerting force for a longer time and the range of motion is larger using more force to release the ball.

What is inertia?

The tendency of an object to resist a change in motion

What do the terms "transfer of forces" and "summation of forces" mean?

The term transfer of force is the principle of transfer of forces, which means that the human body is frequently put into motion by transferring momentum from one body part to the total body mass. The term Summation of forces is the effect of more than one force acting on a body can be found by summing all the forces and taking into account the direction of each.

What force creates weight from mass?

The weight of an object is defined as the force of gravity on the object and may be calculated as the mass times the acceleration of gravity, w = mg. Since the weight is a force, its SI unit is the newton.

How does torque impact on rotational motion?

Torque is the rotational equivalence of force. So, a net torque will cause an object to rotate with an angular acceleration. Because all rotational motions have an axis of rotation, a torque must be defined about a rotational axis. A torque is a force applied to a point on an object about the axis of rotation.

Factors Influencing Projectile Range and Horizontal Distance

Trajectory: Angle of projection Projection speed Relative height of projection

Velocity

Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time.

Horizontal & Vertical Components

Vertical is influenced by gravity No force (neglecting air resistance) affects the horizontal Horizontal relates to distance Vertical relates to maximum height achieved

KINEMATICS SELF-EXPERIMENT #7: Now, let's try an activity in which the force element of the impulse is constrained. Fill several balloons with water so that each one is about the size of a softball. Take these outside to an empty field or empty parking lot and see how far you can throw one without having it break in your hand. If you exert too large a force against the balloon, it will break. To throw the balloon far, you must maximize the duration of force application during the throw, while limiting the size of the force you exert against the balloon so that it doesn't break. Don't constrain your technique to what you perceive as normal throwing styles. Remember, the best technique will be the one in which you accelerate the balloon for the longest possible time while applying the greatest (but non-balloon-breaking) force. What do we call this concept--that of applying a given force over a longer duration?

We call this concept Impulse which is the force over time. This concept has to do with newtons second law with momentum.

1. How are weight and mass related?

Weight and mass are related because mass is a measurement of the amount of matter in an object or athlete. Weight is a measure of how gravity affects the mass.

How are weight and mass related?

Weight is equal to the force of gravity on an object and is proportional to an object's mass.

FRICTION SELF-EXPERIMENT #1: Let's do some experimentation to learn more about friction. Place a book on a flat horizontal surface such as a desk or table top. Now push sideways against the book and feel how much force you can exert before the book begins to move. What force resists the force that you exert on the book and prevents the book from sliding? Put another book on top of the original book and push again (see figure). Can you push with a greater force before the books begin to move? Add another book and push again. Can you push with an even greater force now? Why?

What force resists the force that you exert on the book and prevents the book from sliding? The force of friction prevents the book from sliding on the table. Can you push with a greater force before the books begin to move? Yes you can push with a greater force before the book begin to move on the table. Can you push with an even greater force now? Why? Yes, I can push with an even greater force because the force of friction is proportional to the weight of the object meaning with a heavier weight the more force is needed to move the object.

TORQUE SELF-EXPERIMENT #1: Place a book flat on a table or desk. Using two fingers (or a pencil), strike the book on its side to create a force directed through the center of gravity of the book (see figure). (If you could balance the book on a pencil point, the book's center of gravity would he vertically above this point of balance. For now, consider the center of gravity of the book as the center of the book.) What happens as a result of the force you exerted on the book? Now try the experiment once again, only this time hit the book with your fingers or a pencil so that the force is not directed through the book's center of gravity (see figure). What happens? Now repeat the first experiment. Strike the book so that the force your fingers create is directed through the center of gravity of the book. Do it again, only this time, direct the force so its line of action is just off center, causing the force to be an eccentric force. Repeat the experiment several times, each time striking the book so the line of action of the force is farther from the book's center of gravity. Try to keep the size of the force the same in each trial. What happens? To reinforce this concept, try the experiment again. Apply a pair of forces (a force couple) to the book at either end of the book and in opposite directions. Do it again, only this time move your hands so the distance between them and the forces they apply to the book are not as great. Repeat this a number of times, so that each time the lines of application of the forces move closer and closer together until finally the forces are over one another. What happens?

What happens as a result of the force you exerted on the book? When you strike the book in the center of its gravity it causes the book to have a linear motion. The book moves forward straight. Now try the experiment once again, only this time hit the book with your fingers or a pencil so that the force is not directed through the book's center of gravity (see figure). What happens? As the strike moves farther from the books center of gravity, the more the book turns when it is pushed. This causes and angular rotation. Repeat the experiment several times, each time striking the book so the line of action of the force is farther from the book's center of gravity. Try to keep the size of the force the same in each trial. What happens? As the strike moves farther from the books center of gravity, the more the book turns when it is pushed. This causes and angular rotation. As the book is pushed farther from the center, there is an increase in the angular rotation of the book and a decrease in the linear movement of the book. Repeat this a number of times, so that each time the lines of application of the forces move closer and closer together until finally the forces are over one another. What happens? The farther the forces are from each other the easier it is to rotate the book. When the forces are almost in line with each other, there is no rotation of the book because the forces are equal and opposite acting in a similar location in relation to the center of gravity.

TORQUE SELF-EXPERIMENT #3: Let's try another example. Clear the pennies off the ruler. Now stack four pennies on the ruler 3 in. to the left of the eraser. What net torque do these pennies create about the eraser? Four pennies times 3 in. is 12 p x in. of torque in the counterclockwise direction about an axis through the eraser. If you only had two pennies left to use to balance the ruler, where would you stack them?

What net torque do these pennies create about the eraser? Four pennies' times 3 in. is 12 p x in. of torque in the counterclockwise direction. If you only had two pennies left to use to balance the ruler, where would you stack them? If I only had 2 pennies left to use to balance the ruler, I would stack them on the end of the ruler. Two pennies x 6 inches from the eraser would also give 12 p x in which would balance out the ruler.

ANGULAR KINEMATICS SELF-EXPERIMENT #2: Try this experiment to demonstrate the relationship between linear velocity, angular velocity, and radius. Take out the ruler you used previously and balance it on an eraser (or something else that will balance it). This point will be the pivot point or axis of rotation of the ruler. Line up five pennies in a row on the ruler at distances of 2 in., 4 in., 6 in, 8 in., and 10 in. Each penny should be marked so that you can tell the difference among the pennies. Now strike the ruler on the side without the pennies so that it swings. Which penny went the farthest and fastest? Why? Did each penny have the same angular velocity? The same linear velocity?

When doing this experiment, I found that penny B went the farthest the fastest. It went the farthest the fastest because of its location on the ruler and the central point in relation to the striking point. No each penny did not have the same angular velocity because they were all in different locations on the ruler. No, the linear velocity is not the same.

ANGULAR KINEMATICS SELF-EXPERIMENT #3: Throw a pen up into the air and give it a flip as you release it so it rotates end over end. As the pen falls, does its angular velocity change? Does its rotation speed up or slow down after you've released it? Does the axis of rotation change direction? What happens if you throw the pen straight up without it rotating (see figure below)? Will it rotate at some point as it falls?

When the pen falls the angular displacement does not change. When it is thrown, it tends to stay at the same pace and not speed up or slow down when falling. The axis of rotation does change because the center of the pen is being changed when thrown, going from up to down. When you throw the pen straight in the air without rotating it, it will go up straight and fall straight. When thrown in the air straight, It will never rotate and fall because nothing is acting on it to cause it to rotate during the fall.

KINEMATICS SELF-EXPERIMENT #2: Now let's try to describe the motion of a ball thrown up straight (i.e., vertically) into the air. Let's use the terms we have learned--displacement, velocity, and acceleration. If we set up a coordinate system with the x-axis oriented horizontally in the direction of the horizontal motion of the ball and the y-axis oriented vertically, how would you describe the vertical motion of the ball? Let's consider the positive direction along the y-axis (vertical axis) as upward. Is the ball speeding up or slowing down as it goes up? What happens when the ball reaches its peak? Now, throw a ball in the air from one hand to the other. If we resolve the motion of the ball into horizontal and vertical components, what forces are acting on the ball vertically and horizontally?

When thrown straight up into the air the ball would first have a positive displacement in the y-direction when going up and a negative displacement in the y-direction when the ball is falling back down. If the ball is caught in the same spot as the original position before the ball was thrown, then the ball will have a total displacement of zero. As the ball is being thrown upwards the velocity is positive in the y-direction with a negative acceleration meaning that the ball is slowing down as it goes upward in the y-direction. This is because gravity is acting on the ball causing it to slow down until the ball reaches its peak where it has a velocity of zero before falling back down again with a negative velocity and a negative acceleration because the ball is speeding up in the downward direction as the ball falls downward. When a ball is being thrown from one hand to the other the forces acting on the ball horizontally are a horizontal velocity and acceleration in the direction the ball is being thrown, as well as a displacement between both hands. Vertically, initially the velocity will be positive with a negative acceleration until it reaches the peak where the velocity becomes zero. After that the velocity and acceleration will be negative in the y direction. During this process, there is a total vertical displacement of zero because both hands are on the point on the y axis.

KINEMATICS SELF-EXPERIMENT #8: Stand on a chair. Now jump off the chair and land on your feet. How did you reduce the impact force? What did this do in terms of your time of impact? What did this do to reduce the time of impact? Fill a few more water balloons and take them outside. With a friend, play a game of catch with a water balloon. See how far apart you can get from one another and still catch the balloon intact. If you can't find a friend willing to take part in this activity, play catch by yourself. Throw a balloon up in the air and try to catch it without breaking it. Try to throw it higher and higher. What did you do the higher you threw the balloon in the air?

When you jump off a chair, to reduce the impact of force you would bend knees upon impact. In terms of time of impact, when bending your knees, you lengthen the time of impact because of impulse in the change of time over momentum. This reduced the time because the bend of your knees increased the time interval over the change in momentum. When the ball is thrown higher in the air, when you catch the ball, to keep it intact you use momentum when catching it to soften the landing. So, in this example, when catching the balloon, you would soften the impact by continuing the motion to reduce the likeliness of the balloon breaking from a hard stop of a catch.

KINEMATICS SELF-EXPERIMENT #4: Try to find an elevator at UNH, or look for a tall building somewhere locally. What happens when you ride up an elevator? How does it feel when the elevator starts up? Do you feel heavier or lighter? When the elevator is between floors, do you feel any heavier or lighter? What about when the elevator comes to a stop at an upper floor? Do you feel heavier or lighter as the elevator slows down? Explain these phenomena based on Newton's laws and all of the external forces acting on the system. If you can, bring a scale with you on your journey. What happens to your weight reading on the scale during each part of the ride up the elevator. Finally, what happens when you ride the elevator down rather than up?

When you ride an elevator up according to newtons first law, the force of the elevator on your feet in the upwards direction will cause you to travel at the same velocity as the elevator. When the elevator starts up, you feel the force of gravity pulling you down as you move up with the elevator because gravity is opposing your motion making you feel heavier. When the elevator is between floors you no longer feel heavier because the force of gravity is no longer opposing your motion because you have come to rest. As the elevator slows down you feel lighter because your inertia is still pulling you at the same velocity and direction as when the elevator was moving originally at the faster velocity. Likewise, when you stop at an upper floor there is a split second where you feel lighter than before because your inertia is still pulling you in that direction for a short period of time even when the elevator stops moving. After the short period, you return to the normal weight. When you ride an elevator in the upwards direction, the scale reads heavier than your actual weight because the force of gravity Is opposing the force of the elevator causing both forces to impact your weight. When you are going down in the elevator, the scale will read lighter because the force of the elevator is acting in the same direction as the force of gravity.

FRICTION SELF-EXPERIMENT #2: Let's observe the difference between the frictions of a book on the table and a shoe on the table. Place the book on the table and put an athletic shoe on top of it. Push the book back and forth across the table and get a feeling for how large the dynamic and static friction forces are. Now put the shoe on the table, sole down, and place the book on top of it. Push the shoe back and forth across the table and get a feeling for how large the dynamic and static friction forces are. Which produced larger frictional forces with the table, the book or the shoe? What changed between the two conditions?

Which produced larger frictional forces with the table, the book or the shoe? The one that produced larger frictional forces with the table was the shoe with the book on top of it. What changed between the two conditions? The grip of the object on the table was the factor that changed the outcome. When the book was on the table it was smooth and easy to move but when the shoe was on the table, the shoe had a rougher texture allowing it to have better grip on the table and more friction.

TORQUE SELF-EXPERIMENT #2: Take out the ruler, eraser, and pennies. First, balance the ruler on the edge of the eraser. By our definition of center of gravity as "the point of balance," the center of gravity of the ruler must lie above the points of support provided by the edge of the eraser. The counterclockwise torque created by the weight of the ruler to the left of the eraser balances the clockwise torque created by the weight of the ruler to the right of the eraser. Now make two stacks of pennies with four pennies in each stack. Place one stack 1 in. to the left of the eraser and the other stack 1 in. to the right of the eraser so that the ruler remains balanced. The center of gravity of the pennies and the ruler is still above the eraser. Now slide the right stack of pennies 1 in. to the right and move the eraser so that the ruler remains in equilibrium. Which way did you have to move the eraser? Which way did the center of gravity move? Now move the right stack of pennies all the way to the right end of the ruler and move the eraser so that the ruler remains balanced. Again, you had to move the eraser in what direction?

Which way did you have to move the eraser? Which way did the center of gravity move? When the pennies were moved to the right an inch, I had to move the eraser to the right as well. This means that the center of gravity moved to the right because the eraser represents the center of gravity. Again, you had to move the eraser in what direction? When you move the pennies all the way to the end of the ruler on the right, the eraser needs to move to the right as well to keep the center of gravity in equilibrium.

Define force as it relates to motion.

a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a push or a pull.

First-class lever

a lever for which the muscle force and resistive force act on opposite sides of the fulcrum Lever A is the first-class lever which is positioned between the resistance and the force. An example of this type of lever is an athlete using a leg press machine or any type of weight training machine. With the leg press machine, the athlete is applying force with their legs on one side of the axis and the weight stack as the resistance applies its own force on the other.

What is meant by "Center of Gravity"

a point from which the weight of a body or system may be considered to act. In uniform gravity it is the same as the center of mass.

Law #2

acceleration (gaining speed) happens when a force acts on a mass (object) The more force you use to a hit a tennis ball, the more reaction force your arm receives from the racket. Every time your feet hit the ground when you are running, the ground hits your feet with an equal and opposite force Law of acceleration: The acceleration of objects or athletes is proportional to the force that acts on them and is inversely proportional to their mass. A more massive athlete accelerates less than an athlete with less mass when the same force is applied to both.

Is deceleration the same as acceleration?

acceleration is considered to describe an increase or positive change of speed or velocity. On the other hand, deceleration is considered to describe a decrease or negative change of speed or velocity.

Gravity

acts as a resistive force to slow an upward-directed object; becomes a motive force acting in a downward direction, increasing object's speed.

aerodynamic forces include : (1)________________, and (2)________________.

drag is the force component parallel to the direction of relative motion, lift is the force component perpendicular to the direction of relative motion.

Define Newton's Three Laws of Motion Law #1

every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. when you pick up a stationary ball and throw it, changing its motion with force, or when a ball is hit by the bat, changing the ball's direction initially dictated by the throw from the pitcher. Law of Inertia- all athletes and objects have mass and therefore have inertia. Their inertia is expressed by a desire to remain at rest. If a force is applied against them to get them moving, their inertia gives them the desire to travel at the same velocity in a straight line.

Drag Force (air resistance)

is always against the direction of the object's motion. Air-drag force is increased with the velocity.

As a point moves further away from the axis of rotation what happens to that point in terms of distance traveled and velocity?

it increases

How does force (torque) relate to the concept of "Mechanical Advantage."

the advantage gained by the use of a mechanism in transmitting force specifically : the ratio of the force that performs the useful work of a machine to the force that is applied to the machine

kinetic energy

the energy an object has due to its motion Any object in motion is using kinetic energy: a person walking, a thrown baseball, a crumb falling from a table, and a charged particle in an electric field are all examples of kinetic energy at work.

Second class lever

the load is between the fulcrum and the input force; never changes the direction of the input force Lever R is the second-class lever which is positioned between the axis and the force. The second-class lever is characterized by the force and resistance being on the same side of the axis. An example of a second-class lever is when an athlete performs a bench press on a weight machine.

Friction

the resistance that one surface or object encounters when moving over another.