Download Review for Forces - The Russell Elementary Science Experience

Review for Forces
I. Vocabulary
1. A force is any push or pull that causes an object to move, stops moving, or
changes direction only when a force acts on it.
2. Friction is a force that opposes, or acts against, motion when two surfaces rub
against each other.
3. Magnetism is the force of repulsion (pushing) or attraction (pulling) between
poles of magnets.
4. Gravitation is the force that pulls all objects in the universe toward one another.
5. Balanced forces are forces that are equal in size and opposite in direction.
6. Unbalanced forces are forces that occur when one force is greater than its
opposite force.
II. Possible Questions
1.
2.
3.
4.
What is the biggest magnet that you know of? The Earth
What happens when opposite poles in a magnet come together? They attract.
What happens when the same poles in a magnet come together? They repel.
What happens when two rough surfaces are rubbed against each other?
Smoothed surfaces? The rough surfaces produce more friction than smooth
surfaces do. The rougher the surface the more friction that will be created. The
smoother the surface the less friction that will be created.
5. How does the mass of objects affect the strength of the gravitational pull between
them? The greater the mass of an object, the greater the gravitational pull exists.
6. How does the distance between two objects affect the strength of the gravitation
between them? The closer they are, the greater the gravitational force.
7. What keeps the moon in orbit around the Earth? Gravity
8. What will happen if forces of equal size collide together if the objects are still, or if
they are in motion coming from opposite directions? They cancel each other out
and no movement occurs in still objects, or change in movement occurs in objects
that have motion in the opposite direction.
9. What will happen if two unbalanced force act on each other? Both objects will
move in the direction of the greater force.
10.
What starts an object moving or stops it if it is already moving? Another
force acting on the object.
11.
What force keeps the earth and all the other eight planets rotating in their
orbits around the Sun?
12.
What does the basic law of science “Forces always act in pairs” mean? When
one object acts on a second object, the second object also acts on the first object.
III. Be able to write down the three forces that affect you everyday. Gravity,
Friction, and Magnetism
IV. Be able to work out problems dealing with forces to figure out the net force.
pg. F14
Problems for exam
1. Suppose two people who are moving a refrigerator push on the same side. Each
pushes with a force of 120 Newtons (N) toward the right. What would be the net
force?
120 N + 120 N = 240 N
The net force on the refrigerator equals 240 Newtons to the right.
2. Suppose the force of friction resisting the movement of the refrigerator is 100
Newtons. This force acts in a direction opposite to the force acting to the right on
the refrigerator. 240 N – 100 N = 140 N
The net force on the refrigerator equals 140 Newtons to the right.
3. If two equal forces act on an object in opposite directions, the net force will be
balanced and the object’s motion will not change.
4. What is the net force when a force of 100 Newtons pushes against a force of
friction of 80 Newtons? 100 N – 80 N = 20N
V. Be able to predict the direction in which the object will move if a certain
force is added to it.