Motion & Forces Cont.

Multiple Choice

When a cannon fires a cannonball we observe Newton's third law. Which is the reaction force?

• The cannon moving forward

• The cannon moving backwards

• The cannonball moving backwards

• The cannonball moving forward

​The closer the distance, the stronger the effect

Multiple Choice

8. What is true of non-contact forces?

• They are always stronger than contact forces

• They always drive two objects farther apart

• They become weaker with distance

• They can not make two objects touch

Multiple Choice

Which model has greater gravitational attraction (if any)

• Model A
• Model B
• Both Model A and Model B (same gravity)

Multiple Choice

Which system has the greater gravitational attraction between the two objects (if any)?

• System A
• System B
• Same gravitational attraction fro System A and System B

Why don't the cars slide down the hill?

WHAT IS FRICTION?

Friction is a force that resists the

motion of two surfaces that are
touching.

When a moving object comes in contact with another object, friction is the opposing force that slows or
stops the moving object.

WHAT IS FRICTION?

*Sliding...resists objects while they are moving

*Fluid…air or water
*Rolling …wheel, roller, or ball

*Static. Prevents objects sliding

Friction

• Friction is a force that appears when two objects are in contact (touching)

• When the boy pushes the box, friction pushes back in the opposite direction

• The box will only move if the pushing force is greater than the friction force

The direction of friction

• Friction acts to oppose motion

• To draw the force arrow to represent friction, we need to first think: "which way is the object trying to move?"

• In this picture, the heavy box will try to move down the hill. Therefore, friction acts up the slope.

Multiple Choice

True of False?
An object's inertia is effected by its mass.

• False
• True

Multiple Choice

7. Acceleration occurs when an object is subjected to a(n):

• Force

• Balanced force

• Unbalanced force

• Contact force

Multiple Choice

Which has the MOST inertia?

Multiple Choice

What is the net force?

• 20 N 
• 0 N 
• 400 N 
• 40 N 

Multiple Choice

Calculate the Net Force. 

• 60N, Left 
• 40N, Right 
• 0N
• 60N, Right