Forces and Friction Test

What is a force?

A force is any influence, such as a push or a pull, that causes an object to move or change its speed, direction, or shape.

What can force do to moving objects?

Stop it from moving.

What can force do to stationary objects?

Cause it to move.

What is the SI unit for force?

Newtons (or N).

What is net force?

The net force on an object is the combination of all forces acting on the object. This determines if and how an object will accelerate.

What is the net force in this image?

100 N ←

What is the net force in this image?

50 N ←

What is the net force in this image?

90 N →

What is magnitude?

An amount or strength (distance).

How does magnitude relate to net force?

The net force is the magnitude + the direction.

What is elasticity?

The ability of a material to return to its original shape after being stretched or compressed.

Explain projectile motion.

When something is thrown, it is propelled forward and the gravity is pulling it down. This causes a downward trajectory.

Explain orbital motion.

The earth is orbiting the sun. This happens because the sun's gravity pulls the Earth towards the sun while at the same time the Earth is moving forward. The two forces balance out creating an orbit.

Define friction.

Friction is the force that opposes the motion between two surfaces that touch.

Why does friction occur?

No surface is completely smooth. So, friction is caused by the tiny bumps and dips on surfaces catching each other when they touch.

What are the four types of friction?

1. Sliding Friction: pushing an object across a surface

2. Rolling Friction: between wheels and a surface

3. Fluid Friction: opposes the motion of objects traveling through a fluid (air or water)

4. Static friction: force applied to an object preventing the object from moving.

What two factors affect the frictional force between objects?

1. Roughness (of the surfaces)

2. Force (pushing the surfaces together)

Is the following force balanced or unbalanced? (You can answer with a “B” or a “U”).

A book sitting on a table.

B

Is the following force balanced or unbalanced? (You can answer with a “B” or a “U”).

A game of tug-a-war where neither team is moving.

B

Is the following force balanced or unbalanced? (You can answer with a “B” or a “U”).

The girl is riding a skateboard.

U

What is the traditional definition of gravity?

A force of attraction between things that have mass.

What two factors influence the strength of gravity between two objects?

Mass and distance.

What is the relationship between weight and gravity?

Weight measures the force of gravity pulling downward on an object. The more gravity the more something weighs.

What is Newton’s Law of Universal Gravitation?

Gravity is a force of attraction between all objects in the universe and the strength of gravity is greater when masses of objects are greater or distances between objects are shorter.

What is Einstein’s explanation of gravity?

Gravity happens because of the warping of space and time. The more massive a body is, the more it causes space-time to curve. Imagine a bowling ball pressing down on a trampoline. Now imagine placing a lighter ball at the edge of the trampoline. The lighter ball will roll down toward the bowling ball.

What is the SI unit for mass?

Kilogram (kg)

What is the SI unit for weight?

Newton (or N)