Download Testing Balanced and Unbalanced Forces 15.2 Directions

Testing Balanced and Unbalanced Forces
15.2
Directions: Following the procedures below. Write down the purpose and answer any of the questions on
a sheet of notebook paper. Remember to include part of the question in your answer.
Purpose: How is an unbalanced force different from a balanced force?
Procedure:
1. Place the white paper in the bottom of the plastic box. Put
the metal ring on top of the paper with the lip up, as if you
were putting the metal ring on a jar. Trace an outline of the
OUTSIDE of the ring onto the paper. Remove the metal ring
from the paper. Mark 4 points at equal distance going around
3 1
the circle. Number the marks 1 to 4 going clockwise, like the
1 picture to the right.
2
2. Place the metal ring on the circle, again with the lip up. Place
1 the marble inside the metal ring. Without moving the metal
ring, describe the motion of the marble. (How is the marble
moving right now)
3. Inertia: Objects will not change their motion until an unbalance force acts on them. Use the ring to
move the marble in a clockwise circle. Keep the ring on the paper at-all-times. Record your
observations. What is happening to the marble?
4. Balanced force are forces that are the same, but are pulling or pushing in opposite directions.
Balanced forces do not change the motion of an object. How does the metal ring produce unbalanced
forces that influence the marble’s motion? Why is the marble not moving to the walls of the plastic
container?
5. Make a prediction about what will happen if you lift the ring (remove the unbalanced force)
6. Move the marble in clockwise circle again lifting the ring. What happens to the marble?
7. While having the marble move in clockwise circles
Trial
Number the marble left the
using the ring; try to pick up the ring when the marble
circle at:
at mark #2. Record in the table below which mark #
the marble leave the hand drawn circle at: ALSO
1
draw the path of the marble as it left the circle until
2
the marble hit the wall of the container on the sheet of
paper in the box.
3
8. What did you notice about the path of the marble?
Did the marble leave the circle at number 1 exactly?
9. While having the marble move in clockwise circles using the ring; try to pick up the ring when the
marble at mark #4. Record in the table below which mark # the marble leave the hand drawn circle at:
ALSO draw the path of the marble as it left the circle,
on the sheet of paper, until the marble hit the wall of
Trial
Number the marble left the
the container.
circle at:
10. What did you notice about the path of the marble?
1
11. Like the marble, the planets move forward due to
inertia and inward due to an unbalanced force.
2
Together, these forces cause the planets’ paths to
3
curve. What is the unbalanced force that keeps the
planets in orbit?
12. What would happen to the planets without this unbalanced force?
13. What evidence do you have to support your answer to question 12?
4 Orbital Motion
How does gravity govern orbital motion in the solar system? The Sun’s gravity continuously pulls
the planets toward the Sun. But the planets also have a natural tendency to move forward in their orbits at
a constant speed and in a straight line until acted upon by an outside force. These two motions – forward
motion and motion toward the Sun under the influence of gravity – keep the planets traveling in curved
paths in elliptical orbits around the Sun. The greater the gravitational force pulling on a planet and the
greater its tendency to move forward, the greater its orbital velocity. Without the Sun’s gravity, these
solar system bodies would each move out through space in a straight line.
The planets orbit the Sun in a counterclockwise direction (as seen form Earth’s North Pole) with
those planes closest to the Sun traveling the shortest distance. Because the planets an the Sun originally
were formed from the same rotating disk of dust an gas, it is logical that the counterclockwise direction of
planetary revolution coincides with the Sun’s counterclockwise rotation. Most of the planets also rotate in
a counterclockwise direction. Venus is an exception because it is tilted nearly 180-˚ on its axis. This
means that from Earth’s north pole, Venus appears to rotate in a clockwise, or retrograde, direction.
Unbalanced Forces Defined
Unbalanced forces are forces that cause a change in the motion of an
object. Learn more about how to identify balanced and unbalanced
forces through several examples and test your knowledge with quiz
questions.
Any push or pull is a force. To describe a force, you must know two
things. You must know the size of the force and the direction of the
force. Suppose two teams are playing tug of war. Each team is pulling
with equal force, but in opposite directions. Neither team can make the
other team move. Forces that are equal in size but opposite in direction are called balanced forces.
Balanced forces do not cause a change in motion. When balanced forces
act on an object at rest, the object will not move. If you push against a wall,
the wall pushes back with an equal but opposite force. Neither you nor the
wall will move. Forces that cause a change in the motion of an object are
unbalanced forces.
Unbalanced forces are not equal and opposite. Suppose that one of the
teams in tug of war pulls harder than the other team. The forces would no
longer be equal. One team would be able to pull the other team in the
direction of the larger force.
Force and Motion
More than one force can act on an object at the same time. If you hold a paper clip near a magnet, you, the
magnet and gravity all exert forces on the paper clip. The combination of all the forces acting on an object
is the net force. When more than one force is acting on an object, the net force determines the motion of
the object. In this example, the paper clip is not moving, so the net force is zero.
How do forces combine to form the net force? If the forces are in the same direction, they add together to
form the net force. Suppose you and a friend are asked to move a piano for the music teacher. To do this,
you pull on one end of the piano, and your friend pushes on the other end. Together, your forces add up to
enough force to move the piano.
This is because your forces are in
the same direction. Because the
forces are in the same direction,
they can be added together to
determine the net force. In this
case, the net force is 45 N, which is
plenty to move a piano - if it is on
wheels, that is!
If two forces are in opposite directions, then the net force is the difference between the two forces, and it
is in the direction of the larger force. Consider two dogs playing tug of war with a short piece of rope.
Each is exerting a force, but in opposite directions.
Notice that the dog on the left is pulling with a force of 10 N, and the dog on the right is pulling with a
force of 12 N. Which dog do you think will win the tug of war? Because the forces are in opposite
directions, the net force is determined by subtracting the smaller force from the larger one. In this case,
the net force is 2 N in the direction of the dog on the right. Give that dog a dog biscuit!
Unbalanced Forces in Action
Unbalanced forces can change the motion of an object in two ways. When unbalanced forces act on an
object at rest, the object will move. In two examples mentioned earlier, the net force on the object is
greater than zero. Unbalanced forces produced change in motion (acceleration) and the receivers of the
forces - the piano and the rope - moved. Unbalanced forces are necessary to cause a nonmoving object to
start moving.
Second, when unbalanced forces act on a moving object, the velocity of the object
will change. Remember that a change in velocity means a change in speed,
direction or both speed and direction. For example, consider a soccer game. The
soccer ball is already moving when it is passed from one player to another. When
the ball reaches the second player, the player exerts an unbalanced force - a kick on the ball. After the kick, the ball moves in a new direction and with a new
speed.
Examples of Unbalanced Forces
A force can act on an object without causing it to accelerate if other forces cancel the push or pull of the
force. Look at this figure. If you and your friend push on a door with the same force in opposite
directions, the door does not move. Because you both exert forces of the same size in opposite directions
of the door, the two forces
cancel each other.
Two or more forces exerted
on an object are balanced if
their effects cancel each other,
and they do not cause a
change in the object's motion.
If the forces on an object are
balanced, the net force is
zero. If the forces are
unbalanced forces, the effects
don't cancel each other. Any
time the forces acting on an
object are unbalanced, the net
force is not zero, and the
motion of the object changes.
This figure demonstrates that horizontal force acting on a refrigerator is F. If F is
the only force acting on the refrigerator, then it will accelerate horizontally (a). The
free-body diagram shows the net horizontal force acting on the refrigerator (b).
This figure shows that when two people apply equal,
forces to a refrigerator, these two forces cancel each other,
zero. This means there cannot be any horizontal
If you stand on a skateboard and someone gives you a
skateboard will start moving. You began to move when the
object at rest - like you on your skateboard - remains at rest
force acts on it and causes it to move.
oppositely directed
and the net force equals
acceleration (a).
push, then you and your
force was applied. An
unless an unbalanced
Question
14. What is a balanced force?
15. What is an unbalanced force?
16. If Mr. Kusibob pushes on a chair with a force of 10 N and Mr. Ragaller pushes in the opposite
direction with a force of 3 N. Which way will the chair move?
17. If Mr. Glennon and Mr. Ragaller push a chair in the same direction each with force of 6 N and Mr.
Kusibob pushes the chair in the opposite direction with a force of 10 N, which way will the chair
move?
18. Write a couple of sentences answering the purpose question to this inquiry.