Force and Newton’s Laws Study Guide
1. State the law of universal gravitation.
The force of gravity acts between all objects in the universe.
2. What is weight?
Weight is the measure of the force of gravity on an object.
3. Why do scientists prefer to describe matter by its mass
instead of weight?
Weight can change with location but mass will stay
constant. Mass is how much matter is in an object.
4. What are the two factors that affect the strength of gravity?
a. mass
b. distance
5. How do mass and distance affect the gravitational
attraction between two objects?
The more mass an object has, the greater the strength of its
gravitational force; the greater the distance between two
objects, the weaker the gravitational forces between them.
6. Using a Venn diagram, compare and contrast balanced and
unbalanced forces. You should have a total of 4 contrasts
and 2 similarities.
Balanced – net force equals zero, does NOT change an
object’s motion
Same – push or pull, strength and direction
Unbalanced – net force does NOT equal zero, changes an
object’s motion
7. Explain static friction and give an example.
Static friction is the friction that acts on objects that are not
moving. Because of static friction, you must use an
unbalanced force to start the motion of a stationary object.
Example – trying to move a stalled car to the side of the
road. The heavier the object, the more static friction it has.
8. Explain sliding friction and give an example.
Sliding friction occurs when two solid surfaces slide over
each other. Sliding friction is caused by the microscopic
roughness of all objects.
Example – throwing sand on an icy patch on the ground to
help your footing.
9. Explain fluid friction and give an example.
Fluid friction occurs when a solid object moves through a
fluid (gas or liquid). This friction is much easier to overcome
than sliding friction. Lubricants are used to help reduce sliding
friction.
Example – water on a water slide, applying oil to a squeaky
gate hinge
10. Explain rolling friction and give an example.
Occurs when an object rolls across a surface. This friction is
much easier to overcome than sliding friction. Rolling
friction reduces the amount of contact between surfaces
because of curved shape of a sphere/circle/
Example – wheels, ball bearings
11. How is a force described?
A force is described by its strength and direction.
12. What is net force?
A combination of all forces acting on an object.
13.How can you find the net force if two forces act in opposite
directions?
You would subtract to find the net force.
14. Define Newton’s laws of motion.
1st Law - An object at rest will stay at rest and an object
moving at a constant velocity (motion) will continue to
move at a constant velocity (motion), unless acted upon
by an unbalanced force. This law is also called the Law of
Inertia.
2nd Law – The acceleration of an object depends upon the
object’s mass and the net force acting on the object.
acceleration = force/mass
3rd Law – For every action there is an equal and opposite
reaction.
15. When an object speeds up, slows down, or changes
direction, why is an unbalanced force involved?
If an unbalanced force was not involved then there would
be no change in the object’s motion.
16.Draw the equation triangle for force, mass, and
acceleration.
Force
mass
acceleration
17. The force of gravity causes all objects near Earth’ surface to
accelerate how fast?
9.8 m/s² or 32 ft/s²
18. What are the SI units for acceleration, force, and mass?
acceleration = m/s²
mass = kg
force = N
19. What two factors affect the force of friction?
a. the types of surfaces involved
b. how hard the surfaces are pressed together
20.
Identify one product of friction?
Heat, wear, slows objects down
21. Two children are moving a wagon full of baseball
equipment that has a mass of 35 kg. One child pulls with a
force of 35 N and the other one pushes with a force of 60
N. The frictional force between the wagon and the ground
is 20 N. What is the net force acting on the wagon? What
is the forward acceleration of the wagon? Diagram the
information in this question and show your work!!!
35 N + 60 N = 95 N
95 N – 20 N = 75 N of net force on the wagon
acceleration = 75 N / 35 kg
acceleration = 2.1 m/s²
22. Identify the action – reaction forces that are present.
Walking –
Action Force – Your foot pushes down and back on
the ground
Reaction Force – The ground pushes your foot up
and forward
A paddling a kayak –
Action Force – The paddle pulls the water backwards.
Reaction Force – The water pushes back onto the
paddle causing the kayak to move forward.
23. What is the net force acting on a 0.15 kg hockey puck
accelerating at a rate of 12 m/s²? **Show work**
F = ma
F = 0.15 kg X 12 m/s²
F = 1.8 N
24.Thinking of Newton’s second law of motion, what are two
ways to increase the acceleration of an object?
a. Decrease the mass of the object
b. Increase the force acting on the object
25. Define centripetal force.
Any force that causes an object to move in a circular path.
A center seeking force.
26. How does gravity affect objects that are moving
horizontally?
Gravity pulls objects that are moving horizontally toward
the center of the Earth in the same way it pulls a dropped
object.
27. Why can an object have a constant speed and still be
accelerating.
The object could be changing directions.
28. Define inertia.
The tendency of an object to resist a change in its motion.
29. How is mass related to inertia? Give an example.
The greater the mass, the greater the inertia.
Example – An aquarium full of water versus an empty
aquarium. The aquarium with water has more mass so it has
more inertia. Therefore it is harder to move.
30. How does Newton’s first law explain what happens to
passengers when a car stops quickly?
When a car stops quickly a person’s body wants to continue
forward in a straight line even though the car is stopped.
This is the result of a body’s inertia. If a person doesn’t wear
a seat belt their head could hit the dash board or the
windshield.
31.Define momentum.
A characteristic of a moving object that is related to the
mass and velocity of the object.
32. When a rocket is launched, are the forces acting on it
balanced or unbalanced? How do you know?
The forces are unbalanced. I know because the rocket is
accelerating and increasing in altitude. If the forces were
balanced the rocket would still be on the launch pad.
33. Draw a diagram showing the motion of a satellite around
Earth. Label the forces acting on the satellite. Is the satellite
Your drawing should show Earth’s gravitational force
accelerating?
(centripetal force) directed toward the center of the
Earth and perpendicular to the satellite’s motion. The
forward velocity of the satellite is balanced by the
force of gravity (centripetal force) which causes the
object to be “held” in orbit. Remember the satellite is
continuously falling around the Earth.
The satellite is accelerating because it is changing
direction.