EPHE 341 - 7. Linear Kinetics 2

Linear Kinetics 1. From Newton's first 2 laws we learned that an ___ is required to change the state of motion of an object (N1 and N2 [F=ma]) and an object in motion has ___ (N1). 2. How does the momentum of an object change? 3. The ___ that the object is accelerating and the ____ of the acceleration will determine the velocity of the object. 4. ____ is the area under an acceleration time graph

1. external force ; momentum 2. F=ma (N2) which means that a force will cause an object of a certain mass to accelerate. • Therefore force is proportional to acceleration 3. time ; magnitude 4. change in velocity

Friction 1. Static Friction - Consider a crate sitting on the ground 2. As the applied force increases, static force... 3. At the critical point, static force is called the ... 4. If applied force increases further..

1. A force that acts at the surface of contact between two bodies opposite in the direction of motion or impending motion - When a small force is applied to one side of the crate, it remains motionless. The force that opposes the applied force pushing the box forward is the force of static friction 2. increases until a critical point is reached 3. force of maximum static friction 4. the box will begin to slide

Label the Graph from 1-10

1. Static (feet only) 2. Rise to stand 3. Static (stand) 4. Crouch 5. Jump 6. Static (no load) 7. Dropland 8. Static (stand) 9. Sit 10. Static (feet only)

Friction 1. Define 2. Results from the interaction of the ... 3. Dry Friction 4. Fluid Friction 5. Internal 6. Tribology

1. The force resisting the relative motion of solid surfaces. 2. surface area of objects in contact 3. Static, kinetic 4. Lubricated, skin 5. an internal force that resists the movement between the particles of a material. This potential internal movement can be due to either external forces or change in temperature and deformation. 6. The science and engineering of interacting surfaces in relative motion

Static Friction 1. the normal force (N) is equal but opposite the ... 2. The force of friction acts ___ to the surface

1. component of the object's weight acting perpendicular to the surface on which the object is sitting 2. parallel

Friction Remember from our forces lecture, we calculated the perpendicular, and parallel components of gravity on a slant surface The parallel component of gravity will tend to pull the block down the surface. 1. Friction force is required to be ___ of the parallel force or the block would slide down the slope. 2. Friction force is proportional to the ___ and acts..

1. equal and opposite 2. normal force ; perpendicular to it

Linear Kinetics 1. If we want to consider change in momentum we need to ... 2. We know that mΔv is momentum and F = ma, therefore.. 3. Impulse is a measure of.. 4. The net force acting over some time will cause a change in ____ 5. Impulse is the area under a ___ graph

1. multiply both sides by mass 2. ΔP = Ft 3. a force applied for a certain amount of time (impulse (I) = Force (F) x time (t) 4. momentum 5. force time

Linear Kinetics On a force x time graph for a vertical jump.. 1. Weight > ground reaction force - ? 2. The positive impulse stops the ___ and then results in a ... - this = ? 3. Following this, ____ slows the upward motion of the jumper just prior to take-off 4. The height the person jumps is determined by? 5. So why do we add up the 3 different impulses? Why not just the positive one?

1. negative change in momentum 2. positive change in momentum - vertical velocity that results in the jump 3. negative impulse 4. the net impulse - the difference between the total positive impulse and the total negative impulse. 5. we need to account for all of the prior momentum to determine what will happen

Kinetic Friction 1. Define 2. As applied force continues to increase..

1. once the box is in motion, the friction force acting on the box is called kinetic friction 2. kinetic friction remains constant and is always less than the force applied

Friction Static Friction Equation 1. The coefficient of friction indicates?

1. the coefficient of friction indicates the ease of sliding. the greater μ, the less easily one surface will slide on another

Linear Kinetics Impulse-momentum Relationship 1. changes in the momentum of a system depend on (2) 2. therefore an impulse can cause a change in ___ 3. Equations

1. the magnitude of external forces - the time over which the forces act. 2. momentum 3. PIC

Linear Kinetics 1. During human movement we are constantly trying to change the ___ of something. 2. In these activities the force profiles can be explained by the ____ relationship

1. velocity - Walking (change the velocity of our center of gravity) - Sports(change the velocity of our whole body or object) 2. impulse momentum

Linear Kinetics Example Problem During a bobsled race, two crew members push a 90 kg sled with an average force of 100 N over a period of 7 s before jumping in. Assuming that the sled started at rest, what is the bobsled's velocity after 7 seconds?

given in this question: F = 100 N t=7s m = 90 kg Ft = (mv)final - (mv)initial (100 N)(7 s) = (90 kg)v - (90 kg)(0 m/s) v = 7.78 m/s The bobsled's velocity is 7.78 m/s in the direction of force application