Forces

1
Forces

• Chapter 2
• Section 3

2
Forces

• Throwing a baseball, serving a volleyball, or
  just standing up are all examples of forces.
• Force is a push or a pull that one body exerts on
  another. Because of this force, the object moves.
  
• Can you think of any other instances when you
  exert a force on something?

3
Changing Motion

• What happens to the motion of something when you
  apply a force to it?
• The applied force can cause the object to change
  directions.

4
Changing Motion EXAMPLE

• Think of playing volleyball
• The server on the other team serves the ball. The
  ball is heading toward you. You bump the ball.
  The ball now heads up, away from you. By bumping
  the ball, you are applying a force and the ball
  changes direction.

5
Balanced Forces

• Applying a force does not always change the
  velocity.
• Remember velocity speed direction

6
Balanced Forces

• If I have a chair and I push on one side of it
  with a force of 25 N and you push on the other
  side, with a force of 25 N, will the chair move?
• NO
• Why?

25 N
25 N
7
Balanced Forces

• The net force is when two or more forces are
  applied on the same object and at the same time.
  The applied forces combined are called the net
  force.

0
8
Balanced Forces

• The force I apply in one direction plus the force
  you apply in the opposite direction are added
  together.
• 25 N (-25 N) 0
• Because the forces are equal and balancedjust
  like a balanced scalethis is an example of
  balanced forces.

9
Unbalanced Forces

• What does it mean to have something unbalanced?
• Unequal, not the same, different
• How could we have unbalanced forces?

10
Unbalanced Forces

• There are two typescan you guess what they are?
• First type one person applies a force in one
  direction and the other person applies a smaller
  force in the opposite direction.
• Second type both people apply a force in the
  same direction

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Unbalanced Forces
First Type

• If I have a chair and I push on one side of it
  with a force of 50 N and you push on the other
  side, with a force of 25 N, will the chair move?
• YES!
• Which way will it move?
• In the direction I am pushing it.
• Or the direction in which the
• most force is applied
• What is the net force
• in this example?

12
Unbalanced Forces

• 50 N (-25N) 25 N
• These forces are unequal so the forces are
  considered unbalanced forces.

13
Unbalanced Forces
Second Type

• If I push the chair in one direction with 25 N
  force and you push the chair in same direction
  with 25 N force, will the chair move?
• YES
• Why?
• Because the applied net force is
• UNBALANCED!

14
Unbalanced Forces

• The result would be the chair moving in the
  direction it was pushed with a combined force of
  50 N.

25 N

50 N
25 N
15
INERTIA MASS
Chapter 2 Section 3
16
Inertia Mass

• Inertia is the tendency of an object to resist
  any change in its motion.
• An object will continue to move at the same speed
  in the same direction unless acted upon by an
  unbalanced force.

17
Inertia Mass

• If you took a bowling ball and rolled it down the
  street, what would happen? Why?
• Friction is an unbalanced force that causes the
  ball to stop or slow down. Without friction, the
  ball would keep going.

18
Inertia Mass

• Does a bowling ball and a tennis ball have the
  same inertia?
• NO
• Why?

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Inertia Mass

• If you had a tennis racket and I threw a tennis
  ball at you, what would happen?
• If you had a tennis racket and I threw a bowling
  ball at you, what would happen?
• Why could you change the motion of the tennis
  ball but not the motion of the bowling ball?

20
Inertia Mass

• What is mass?
• Mass is the amount of matter in an object.
• A bowling ball has more mass than a tennis ball.
• The greater the mass of an object the greater its
  inertia.

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