Regents Physics

1
Regents Physics

• Agenda
• Circular Motion PowerPoint Notes and Practice
  Problems
• HW p. 166 14,15,16

2
Circular Motion

• Can an object be moving with a constant velocity
  and still be accelerating?
• Yes! If it is moving in a circular path!
• How?

3
Circular Motion
An object that moves with a constant speed
around in a circular path has changing
velocity because its direction is
constantly changing
v
v
r1
r2
v ?d / ?t in circular motion v ?r / ?t ,
this is the velocity
tangent to the circle
v
Demos
?v
v
4
Measuring Speed and Acceleration
A period is one revolution The circumference of
the circle is covered during each revolution
v ?r 2?r
t
T
a v2 4?2r
The acceleration is constant in magnitude but
changes in direction
r
T2
5
What Causes the Acceleration?

• Forces cause accelerations
• So..circular motion must be caused by a force
• Earths orbitcaused by long force of the Suns
  gravity
• Ball attached to a string..force tension in
  string caused acceleration
• Car around track..force of friction!

6
Classifying Acceleration

• The force that causes the acceleration resulting
  in circular motion is called the centripetal
  force
• Centripetal means center seeking..named because
  the acceleration points towards the center of the
  circle

7
So whats centrifugal force?

• Its an imposter!
• The term is used when objects moving in a
  circular path do not experience the centripetal
  force..
• Example..a car making a sharp turn throws its
  passengers to the outside door..why

Because the passenger wants to go in a straight
line!
8
Practice Problem

• A ball is swung in a circular path on a string
  that is 1.5 m long and completes one revolution
  every 0.5 seconds.
• Find the tangential velocity of the ball
• Find the tension force exerted by the string in
  the ball

9
A Force called Torque

• A torque force is a force that is exerted at a
  right angle at a distance from the pivot of a
  rotating rigid body
• The further away from the force acts, the more
  torque is applied as long as it acts at 90
  degrees
• It can act at other angles, however this
  diminishes the torque applied

10
Torque
Pivot
Torque Fapplied x d
Fapplied
11
HW

• Pg. 166 14, 15, 16