Physics: CH.5 TEST
A 60-kilogram boy rolls downhill on a bicycle with a mass of 12 kilograms. What net force is acting on the boy and his bicycle if he accelerates at a rate of 3.25 m/s^2?
234N
How does the inertia of a 200-kg object compare to the inertia of a 400-kg object?
A 200 kg object has ½ has much mass as a 400 kg object, because the 200 kg object has requires ½ as much force to accelerate the 400 kg object.
static
A problem with zero net force and/or no motion /
force
Action with the ability to change an object's motion / any action on a body that causes it to change motion. _____ is a vector and always has a magnitude and direction.
Newton's second law
An object's acceleration is caused by force and resisted by mass / states that the acceleration of an object is directly proportional to the force acting on it an inversely proportional to its mass
To tighten the head of a hammer on its handle, it is banged against a surface as shown to the right. Explain how Newton's first law is involved.
Because the head of the hammer is in motion and wants to continue in motion, even though the motion of the handle has stopped because of the table. Therefore, its motion drives the head of the hammer, down onto the stick.
equilibrium
Condition of zero acceleration / in physics, occurs when the forces on an object are balanced & in chemistry, the state in which the solute in a solution is both dissolving and coming out of solution at the same rate
Are the following statements true or false? Explain your answers using an example: b. To keep an object moving, a force must be applied.
False: All objects want to keep doing what they are doing and tend to resist changes in motion. If they are moving, they tend to keep moving, in the same direction, at the same speed. Force is not necessary to keep an object in motion at constant speed (unless there is friction). An ice-skater can coast for quite a long time because motion at constant speed does not require force. If there were no friction, a skater could coast at constant speed forever. Force is required only to speed up, turn, or stop.
Are the following statements true or false? Explain your answers using an example: Applying a force to an object will make it move.
False: force has the ability to cause movement, but it may not. If you push on a wall it won't move.
What is the difference between the terms "force" and "net force"?
Force is any action on a body that causes it to change motion (force is a push or pull); force is a vector and always has a magnitude and direction. Net force is the amount of force that overcomes an opposing force to cause motion; the net force can be zero if the opposing forces are equal.
pound
Force needed to accelerate 1 kg. at a rate of 4.448 m/s^2 /
newton
Force that accelerates 1 kg. at a rate of 1 m/s^2 / the SI, or metric, unit of force
Newton's third law
Forces always occur in pairs / states that whenever one object exerts a force on another, the second object exerts an equal and opposite force on the first
Explain the difference between mass and weight. State common units for each.
Mass is a measure of an object's inertia; the amount of matter an object has. Weight is a force created by gravity; the gravitational force with which bodies attract each other. Problems may require converting between weight in pounds and mass in kilograms.
How can rolling a bowling ball help you to determine the amount of matter in the ball?
Mass is force divided by acceleration. If we know the acceleration and force, we can figure out the mass.
Newton's first law
Motion of an object tends to be maintained by its inertia / states that an object at rest remains at rest until acted upon by an unbalanced force; an object in motion continues with constant speed and direction in a straight line unless acted in by an unbalanced force.
Name two units commonly used to measure force. How are they related?
Newtons (N) and pounds (lb.). The newton is a smaller unit of force than the pound. A force of one pound is equal to 4.448 newtons.
inertia
The ability of an object to resist acceleration / the resistance of a body to change in motion
State Newton's second law in words. Write an equation expressing the law.
The acceleration of an object is equal to the force you apply divided by the mass of the object. If you apply more force to an object, it accelerates at a higher rate. The equation for this is A = F/m.
If the net force acting on an object is tripled, what happens to its acceleration?
The acceleration will be tripled.
What do motionless objects have in common with objects that are moving in a straight line with constant speed?
The first and second laws apply to single objects. The first law states that an object will remain at rest or in motion at constant speed and direction until acted upon by an external force. The second law states that net force causes acceleration and mass resists acceleration. What both objects have in common is that their forces are balanced.
Explain how the unit of force used by scientists, the newton, is defined
The metric definition of force depends on the acceleration per unit of mass. A force of one newton is exactly the amount of force needed to cause a mass of one kilogram to accelerate at one m/sec^2. We call the unit of force the newton because Newton's second law defines force in the metric system. The newton is a useful way to measure force because it connects force directly to its effect on matter and motion.
What is the difference between dynamic problems and static problems? Give an example of each.
The word dynamic refers to problems involving motion. In dynamics problems, the second law is often used to calculate the acceleration of an object when you know the force and mass. For example, the second law is used to calculate the acceleration of a rocket from the force of the engines and the mass of the rocket. A static problem usually means there is no motion. Most static problems involve using the requirement of zero net force (equilibrium) to determine unknown forces. Engineers who design bridges and buildings solve static problems to calculate how much force cables and beams must carry. The cables and beams can then be designed so that they safely carry the forces that are required. The net force is also zero for motion at constant speed. Constant speed problems are treated like static problems as far as forces are concerned.
net force
Total force acting on an object / the amount of force that overcomes an opposing force to cause motion; the _________ can be zero if the opposing forces are equal
A constant force is applied to a cart, causing it to accelerate. If the mass of the cart of tripled, what change occurs in the acceleration of the cart?
Tripling the mass will reduce the acceleration to 1/3 of its original value.
Are the following statements true or false? Explain your answers using an example: c. A force must be applied to change the direction of a moving object.
True: Forces can be used to change the direction in which an object is moving. The steering wheel and steering system is designed to help you change your motion by changing your direction.
In physics problems, velocities, accelerations, and forces often appear with positive or negative signs. What do those signs indicate?
We often use positive and negative numbers to show the direction of force and acceleration. A common choice is to make speed, force, and acceleration positive when they point right. Speed, force, and acceleration are negative when they point to the left. You can choose which direction is to be positive, but once you choose, be consistent in assigning values to forces and accelerations.
How does the sign of the force applied to an object compare with the sign of the acceleration?
When solving problems, the acceleration always has the same sign as the net force. If the net force is negative, the acceleration is also negative. Careful use of positive and negative values helps keep track of the direction of forces and acceleration.
In Skylab, where objects are said to be weightless, an equal arm balance could not be used to measure the mass of an object. How could you measure the mass of an object in this situation?
You would figure out the force and acceleration.
law of inertia
another term for Newton's first law of motion
action
the first one of the two equal and opposite forces in an action-reaction pair, according to Newton's third law of motion
dynamic
the process of calculating three-dimensional motion from forces and acceleration
locomotion
the progressive movement as of an animal or vehicle
reaction
the second one of the two equal and opposite forces in an action-reaction pair, according to Newton's third law of motion
List at least three parts of an automobile that are designed to overcome the effects of Newton's first law. Briefly explain the function of each.
• Seatbelts & Airbags- You are driving down the highway in your car at 55 mph when the driver in front of you slams on the brakes. You also slam on your brakes to avoid an accident. Your car slows down but the inertia of your body resists the change in motion. Your body tries to continue doing what it was doing- traveling at 55 mph. Luckily your seat belt (and air bag, in an extreme case) are designed to counteract your inertia and slow your body down with the car. • Cup holder- a cup holder does almost the same thing for a cup. Consider what happens if you have a can of soda on the dashboard. What happens to the soda can when you turn sharply to the left? Remember, the soda can was not at rest to begin with. It was moving at the same speed at the car. When your car goes left, the sad can's inertia causes it to keep moving forward. The result is quite a mess. Automobile cup holders are designed to keep the first law from making messes.
