Circular Motion

1

1. If the force exerted by a horse on a cart is
   equal and opposite to the force exerted by a cart
   on the horse, as required by Newtons third law,
   how does the horse manage to move a cart?
2. A soft-drink sits at rest on a table. Which of
   the Newtons laws explains why the upward force
   of the table acting on the can is equal and
   opposite to Earths gravitational force pulling
   down on the can?
3. A book sits at rest on a table. Which force does
   Newtons third law tell us is equal and opposite
   to the gravitational force acting on the book?

2
Circular Motion
An object moving along a circular path at a
constant speed must have a net force acting on
it.
3
It is important to distinguish between adjectives
centripetal (center-seeking) and centrifugal
(center-fleeing). The force, we are discussing ,
the centripetal force, is directed toward the
center of the circle.
4
There is no centrifugal force!!!!
5
A Car, Rounding a Curve
6
Acceleration revisited
7
Velocity and acceleration are perpendicular each
other at each point of this circle.
8
Frequency f (revolutions per second) Period T
1/f ( seconds) The linear velocity of the
object V 2pR/T (meters/second)
9
Dynamics of Uniform Circular Motion
S F ma m V2/R
Centripetal force is just a term, which means
that there is the acceleration pointed to the
center.
10
Skidding on a Curve
11
Banking Corners
12
Projectile Motion
13
When something is thrown or launched near the
Earth surface, it experiences a constant
vertical gravitational force. Motion under these
conditions is called projectile motion.
14
Important The study of projectile motion is
simplified because the motion can be treated as
two mutually independent, perpendicular motions,
one horizontal and the other vertical.
15
Question
Suppose a bullet is fired horizontally from a
pistol and simultaneously another bullet is
dropped from the same height. Which bullet hits
the ground first?
16
(No Transcript)
17
ImportantThe object projected horizontally will
reach the ground in the same time as the object
released vertically from the rest.
18
Object, Thrown Upward
19
You are hunting gorillas with a rifle that shoots
tranquilizer darts. Suddenly you see a gorilla
wearing a bright red button, hanging from a limb.
At the instant, you pull the trigger , the
gorilla lets go of the limb. Where should you
have aimed to hit the gorillas red button?
20
Fast Moving Projectiles Satellites
The Earth satellite is simply a projectile that
falls around the Earth rather than into it.
21
(No Transcript)
22
A common misconception is that satellites
orbiting at high altitudes are free from
gravity. The high altitude only allows the
satellites to go above atmosphere, but they are
in the field of the Earth gravity.
23
Question
A newspaper report reads in part, The space
shuttle orbits Earth at an altitude of nearly 200
miles and is traveling at a speed of 18,000 mph.
The shuttle remains in orbit because the
gravitational force pulling it toward Earth is
balanced by the centrifugal force (the force of
inertia) that is pulling it away from Earth.
Explain why this newspaper should hire a new
reporter.
24
Questions

• What is the force that allows a person on
  roller-blades to turn a corner? What happens if
  this force is not strong enough?
• A child rides on a carousel at constant speed. In
  which direction does each of the following
  vectors point?
• a. velocity
• b. change in velocity
• c. acceleration
• d. net force.

25
Questions
A vine is just strong to support Tarzan when he
is hanging straight down. However, when he tries
to swing from tree to tree, the same vine breaks
at the bottom of the swing. How could it happen?