Download Forces Test Guide - Williamstown Independent Schools

Forces Test Guide
1) What is a force? What is the SI unit of force?
A force is a push or pull. Newtons (N)
2) What is a net force?
Net force is the sum of all the forces acting on an object.
3) Compare balanced and unbalanced forces. How does each affect motion?
Balanced forces are equal in strength and opposite in direction. They cancel out so no
change in motion occurs. Unbalanced forces are not equal in strength and/or do not
cancel out. Unbalanced forces cause a change in motion.
4) What is friction? Describe the 4 types and give examples.
Friction is the force that opposes motion.
Static
Sliding
Fluid
Rolling
5) What factors determine the amount of friction?
The amount of friction is determined by the surfaces in contact.
6) Does the surface area of the object affect friction? No
7) Why is less force needed to keep an object moving than to start it moving?
Less force is needed because the inertia of the object wants to keep it moving. To start
an object moving you have to overcome its wanting to stay still (its inertia)
8) Define inertia and state Newton’s 1st law.
Inertia is the resistance to a change in motion. All objects with mass have inertia. An
object at rest tends to stay at rest and an object in motion remains in motion unless
acted on by an unbalanced force.
9) Define mass, acceleration and state Newton’s 2nd law of motion.
Mass is the amount of matter in an object
Acceleration is the change in velocity of an object.
Newton’s 2nd law gives the relationship between F, m and a (F=ma)
10)
Be able to solve problems using F = ma
11)
Explain how the change in one variable affects the others in F = ma.
a. If force increases then acceleration will increase
b. If the mass is greater then more force will be needed to accelerate it
c. If the mass is greater then the same force will accelerate it less
12)
Compare/contrast mass and weight, including units used.
Mass is the amount of matter. Weight is how that mass is affected by gravity.
13)
What is the force that gives mass its weight on Earth? gravity
14)
What is the value for the acceleration of gravity on Earth? 9.8 m/s2
15)
Describe Newton’s 3rd law of motion. Tell why action-reaction forces don’t cancel
out. For every action force there is an equal reaction force.
16)
Give examples of action-reaction force pairs.
a. When you jump the force you push down on the floor is equal to the force of the
floor pushing back on you
b. A book lying on a table exerts a force down on the table. The table exerts a force
equal pushing back on the book.