Force and Momentum

Question 1

What is a force?

Answer 1

A push or a pull. The unit for force is the Newton (N). Force is a vector.

Question 2

What is a net force?

Answer 2

The sum of all the forces that act on an object.

Question 3

What is an applied force?

Answer 3

A force by an outside actor on an object.

Question 4

What is a friction force?

Answer 4

A force that opposes motion of an object in contact with a substance.

Question 5

What factors determine the magnitude of the friction force?

Answer 5

Friction depends on the nature of the surfaces in contact and the force that pushes the surfaces together.

Question 6

What are four types of friction?

Answer 6

Static friction is the force that opposes the start of motion. Kinetic friction is the force that opposes continuing motion. Sliding/Rolling friction is the force opposing motion when the object rolls on a surface. Drag force (fluid friction) is the force of a fluid (liquid or gas) that opposes the motion of an object passing through it.

Question 7

What is the normal force?

Answer 7

A supportive force that acts perpendicular to the surface upon which an object rests/moves.

Question 8

What is weight?

Answer 8

The force of attraction between an object and the Earth. (Also the force of attraction between an object and the planet/moon it is near.)

Question 9

What is the gravitational force?

Answer 9

The force of attraction between any two objects.

Question 10

What is a spring or elastic force?

Answer 10

A force that restores a spring or elastic object to its equilibrium position.

Question 11

What is inertia?

Answer 11

A measurement of an object’s resistance to changes in its motion.

Question 12

What is momentum?

Answer 12

A measurement of an object’s mass x velocity. The unit for momentum is kg m/s. Momentum is a vector.

Question 13

What is a free-body diagram?

Answer 13

A sketch that indicates the magnitude and direction of all the forces that act on an object.

Question 14

How does an object’s mass relate to its inertia?

Answer 14

Mass is sometimes considered a measurement of an object’s inertia because the more mass that an object has, the larger the force needed to change its motion.

Question 15

When are the forces that act on an object balanced?

Answer 15

The forces on an object are balanced when the net force is 0 Newtons.

Question 16

When are the forces that act on an object unbalanced?

Answer 16

The forces on an object are unbalanced when the net force is not 0 Newtons.

Question 17

What is the effect of balanced forces on an object?

Answer 17

The object will remain in its current motion or remain at rest.

Question 18

What is the effect of unbalanced forces on an object?

Answer 18

The object will accelerate.

Question 19

Two objects are accelerating at the same rate. Which object will have the greater force acting on it, one with a large mass or one with a small mass?

Answer 19

The greater force is needed to keep acceleration constant for the more massive object.

Question 20

The same amount of force is applied to two objects. Which object will accelerate more, one with a large mass or one with a small mass?

Answer 20

The force will accelerate more the object with the smaller mass.

Question 21

What is a force pair?

Answer 21

If object 1 exerts a force on object 2 in one direction, then object 2 will exert an equal force on object 1 only in the opposite direction.

Question 22

Why do force pairs not balance each other?

Answer 22

The force pairs act on different objects.

Question 23

Why can force pairs produce different motion in the different objects?

Answer 23

The motion of objects can differ based on different masses or other forces that act on each object.

Question 24

What is the Law of Conservation of Momentum?

Answer 24

Within a system, objects can transfer momentum to other objects, but the total momentum of all objects will not change.

Question 25

A moving car hits a stationary car at a stop sign. What are the changes in momentum?

Answer 25

The moving car will transfer some of its momentum to the stationary car. If friction is ignored, the momentum of both cars before the crash equals the momentum of the cars after the crash.

Question 26

When a water balloon pops, why does the balloon move but the water momentarily retains the shape of the balloon?

Answer 26

When the balloon pops, the elastic force is enough to overcome the inertial of the balloon. It is not enough to change the shape of the water because the water has more mass and thus greater inertia. The water “wants” to retain the shape of the balloon.