28
Force Study Guide
Balanced/Unbalanced Forces
1. How do unbalanced forces acting on an object affect the object’s motion?
2.
A person throws a ball up into the air. The diagram above shows the ball’s position in the air at 1
second intervals. What is happening at the point the ball is at its highest position with regards to
gravity and the force of the throw?
3. Decide whether each of the following is an example of Balanced or Unbalanced forces:
Balanced or Unbalanced: A tug of war game in which no one wins.
Balanced or Unbalanced: A roller coaster going down the first drop.
Balanced or Unbalanced: A car hitting a wall.
Balanced or Unbalanced: A person pushing a shopping cart.
4. Jenny has two identical marbles. She rolls one marble across a concrete surface with a force of 2 N. At the
same time, she rolls the other marble across an icy surface with the same force.
There is a significantly greater frictional force between the first marble and the concrete surface
than between the second marble and the icy surface. How will the increase in friction affect the
distance the first marble travels?
5. Julio and Luis have to move a box containing a 35 kg television from one room of their house to another.
Julio has the ability to push with a force of 250 N while Luis can only push with a force of 100 N.
If both boys pushed the box in the same direction with all the force they could, what would be the
net force on the box, assuming no friction?
6.A boat is moving east with a force of 30 N, the wind is blowing west with a force of 7 N, and the fluid
friction from the water is pushing against the boat with a force of 5 N. What is the net force of the
boat as it travels east?
Friction
7. Decide whether each is an example of Increasing or Decreasing friction:
Increasing or Decreasing: waxing skis
Increasing or Decreasing: adding grease to gears on a bike
Increasing or Decreasing: throwing sand on an icy driveway
Increasing or Decreasing: oiling a squeaky door
8. In the picture above, what does arrow A represent?
9. How does increasing the amount of pressure pushing down on an object affect the friction between the object
and the surface?
10. Newton's first law of motion states that an object will keep a constant speed and direction unless acted upon
by an unbalanced force.
To test this statement, Martin rolled a ball on a long, level street. The ball did not bump into any
object, but it eventually came to a stop. How is this possible?
11. Which picture below illustrates the least amount of friction between the hands?
A
B
C
Gravity
12. The force that causes two objects with mass to be pulled toward each other is called:
D
13. An object has a mass of 2 kg on Earth. What will happen to its mass and weight on the moon, which has less gravity?
14. Four objects are orbiting a star along the same path.
The objects are the same distance from the star and have
the masses shown to the right.
The gravitational force of attraction is weakest
between the star and which object?
15. True or False: Weight is the force of gravity acting on an
object, while mass is the amount of matter in an object.
16. What is the law of universal gravitation?
17. Four weather satellites are orbiting the Earth at a height of 825 kilometers. Some characteristics of the satellites are
collected in the table below.
satellite
length (m) altitude (km) mass (kg)
I.
5.5
825
692
II.
9.8
825
610
III. 4.4 825 840
IV. 5.6 825 903
The Earth’s gravity exerts the greatest for on which satellite? How do you know this?
18. The distance between two objects affects the force of gravity between them. Based only on distance, the
gravity between the sun and which planet would be the weakest?
19. What two factors affect the force of gravity? Describe how each factor affects gravity.
Magnets
20 .Mark opened a box and pulled out the longest, widest magnet. Well, he only tried to pull that bar out. A
smaller magnet stuck to the end of it. He shook the bigger magnet to make the small one fall off. It didn’t.
How would the poles of the magnets line up when Mark picked up the small magnet?
21. A magnet is placed near a pile of steel paper clips. What will most likely occur?
22. Where is the magnetic field of a magnet the strongest?
Inertia
23. The tendency of an object to resist change in its motion is known as
24. Last-minute Louis frantically tried to finish his homework while his mom drove him to school. He placed
his book on his lap and was reaching for a pencil when his mom suddenly slammed on the brakes.
Although Louis stayed buckled in his seat, his book flew forward and crashed into the front
windshield. Name and describe the force most responsible for the book flying forward.
25. A teacher was discussing with the class that a bowling ball has more inertia than a basketball. What physical
property is most likely being compared between the balls to make the bowling ball have more inertia?
26. A student walking quickly while carrying an orange on his lunch tray stops suddenly. What will most likely happen
to the orange? How do you explain this?
27. Which box would you expect to have the most inertia and how do you know?