Transcript Circular Motion

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 Newton’s third law, how does the horse
manage to move a cart?
2. A soft-drink sits at rest on a table. Which of the
Newton’s laws explains why the upward force of the
table acting on the can is equal and opposite to Earth’s
gravitational force pulling down on the can?
3. A book sits at rest on a table. Which force does
Newton’s third law tell us is equal and opposite to the
gravitational force acting on the book?
Circular Motion
An object moving along a circular path at
a constant speed must have a net force
acting on it.
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.
There is no centrifugal force!!!!
A Car, Rounding a Curve
Acceleration revisited
Velocity and acceleration are perpendicular each other at each
point of this circle.
Frequency f (revolutions per second)
Period T = 1/f ( seconds)
The linear velocity of the object
V = 2pR/T (meters/second)
Dynamics of Uniform Circular
Motion
S F = ma = m
2
V /R
Centripetal force is just a term, which means that there is the
acceleration pointed to the center.
Skidding on a Curve
Banking Corners
Projectile Motion
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.
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.
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?
Important:The object projected horizontally
will reach the ground in the same time as
the object released vertically from the rest.
Object, Thrown Upward
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 gorilla’s red
button?
Fast Moving Projectiles: Satellites
The Earth satellite is simply a projectile that
falls around the Earth rather than into it.
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.
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.
Questions
1. What is the force that allows a person on roller-blades to turn a
corner? What happens if this force is not strong enough?
2. 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.
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?