centripetal force

1
2.3 Unbalanced Forces and Acceleration

• centripetal force
• Newtons second law of motion
• Newtons third law of motion
• Acceleration
• Force pairs

2
Unbalanced Forces and Velocity
2.3 Unbalanced Forces and Acceleration

• Unbalanced forces cause accelerations.

• Without the upward normal force exerted by the
  hand, the ball accelerates downward because of
  the unbalanced force of gravity.

3
Unbalanced Forces and Velocity (cont.)
2.3 Unbalanced Forces and Acceleration

• An unbalanced force applied to a moving object in
  the same direction as the motion speeds the
  object up.
• An unbalanced force applied to a moving object in
  the opposite direction as the motion slows the
  object down.
• Friction is applied in the opposite direction and
  slows the sled down.

4
Unbalanced Forces and Velocity (cont.)
2.3 Unbalanced Forces and Acceleration

• Unbalanced forces can also change the direction
  of motion.

• A thrown ball curves downward because of the
  unbalanced force of gravity.

5
Unbalanced Forces and Velocity (cont.)
2.3 Unbalanced Forces and Acceleration

• A ball tied to a string and swung in a horizontal
  circle has circular motion.

• The velocity of the ball changes because the
  direction of motion changes.
• The string exerts an unbalanced force on the ball
  called centripetal force.

6
Unbalanced Forces and Velocity (cont.)
2.3 Unbalanced Forces and Acceleration

• Centripetal force is the force perpendicular to
  the velocity and pulls toward the center of the
  circle.

• The string keeps the ball moving in a circle.
• Unbalanced forces cause an object to speed up,
  slow down, or change direction.

7
Newtons Second Law of Motion
2.3 Unbalanced Forces and Acceleration

• The acceleration of an object equals the net
  force divided by the objects mass.

• Unbalanced forces cause an object to accelerate.

What is Newtons second law of motion?
8
Balanced Forces, Unbalanced Forces, and Newtons
Second Law
2.3 Unbalanced Forces and Acceleration

• If the net force is equal to zero
• the forces are balanced.

• The acceleration is zero.
• The objects motion does not change.

9
Balanced Forces, Unbalanced Forces, and Newtons
Second Law (cont.)
2.3 Unbalanced Forces and Acceleration

• If the net force is not equal to zero
• the forces are unbalanced.

• The acceleration is not zero.
• The object changes motion.

10
Newtons Second Law and Planetary Motion
2.3 Unbalanced Forces and Acceleration

• According the Newtons second law, there must be
  an unbalanced force acting on Earth and the other
  planets.

• The Suns gravity is the centripetal force that
  keeps Earth and the planets moving in a circular
  path around the Sun.

11
Newtons Third Law of Motion
2.3 Unbalanced Forces and Acceleration

• When one object exerts a force on another, the
  second object exerts an equal force in the
  opposite direction.

• The feet exert a force on the ground and the
  ground exerts an equal force on the feet of a
  jumper, causing the jumper to accelerate upward.

12
Force Pairs
2.3 Unbalanced Forces and Acceleration

• The forces that two objects exert on each other
  are called force pairs.

• The pairs are opposite in direction.
• The pairs are equal in magnitude.
• The forces do not cancel out because they act on
  different objects.

13
Action and Reaction
2.3 Unbalanced Forces and Acceleration

• One force in a force pair is called the action
  force.

• The second force in a force pair is called the
  reaction force.
• For every action force there is an opposite and
  equal reaction force.

14
Lesson 3 Review
2.3 Unbalanced Forces and Acceleration
In what direction does the net force of an object
moving with constant speed and in a circular
motion occur? A downward B opposite to the
objects motion C toward the center of the
circle D in the direction of the objects
velocity
15
Lesson 3 Review
2.3 Unbalanced Forces and Acceleration
Acceleration depends on both the force applied
and ____. A distance from the object B speed of
the object C mass of the object D normal force of
the object
16
Lesson 3 Review
2.3 Unbalanced Forces and Acceleration
How does the motion of an object traveling in a
straight line at 5 m/s change if a balanced force
is applied? A The motion does not change. B The
object speeds up. C The object slows down. D The
object travels in a horizontal circle.