2
CIRCULAR MOTION
Think-Pair-Share (10
seconds)
3
Hypothesize what will happen when Mr. A
swings the swing of water in a circle over his head
Experiment
Results
Conclusion
Why didn’t the water fall down on top of my
head when it was upside down?
The water must have been going somewhere else
Centripetal Force
4 Is an object moving in a circle at a
constant speed accelerating? Why?
Yes it is accelerating because it is changing
directions
A force must have been applied to cause the
Going in Circles: Playing
Hockey
5
Try and make this ball go in a circular
motion
Which way did you have to apply the force?
Going in Circles: Spinning
Marble
6
Watch the marble spin down to the
center of the cone?
What caused the ball to move towards the center?
Going in Circles: Marble
Gravitron
7
Ever been on the amusement park ride,
Gravitron?
Why does the marble
Circular Motion
8 When a force perpendicular to the
direction of motion is applied, an object will go into circular motion
Perpendicular means at 90°
This force points to the center of the circular
motion
The force that causes an object to follow a
circular path is called a
CENTRIPETAL FORCE
Centripetal Force
9 Centripetal force is the
push or pull on a
moving object toward the center of its circular path.
Centripetal force is
always a net force.
Centripetal force is
Examples of Centripetal
Force
10
The only force that is exerted
on the whirling can (neglecting gravity) is directed toward the center of circular motion. This is a centripetal force. No
CFU: Identify Centripetal
Force
The two pictures above each show a force.
Which one is the centripetal force? Why?
The Forbidden F-Word
12Centripetal Force and the
Universe
13 Centripetal force keeps the
planets in orbit.
According to Newton’s 1st law,
all masses have inertia and
would like to move at constant speed in a straight line. Earth wants to move straight but it is prevented from doing so due to the sun’s gravity.
The Sun’s gravity is perpendicular
to the direction of Earth’s motion
The sun applies a centripetal
What Would Happen if…
(CFU)
14
The sun just disappeared, where would
the Earth go?
Watch this: Centripetal Cat
Where did the cat fly?
Quick Check
15Question 1 of 6
16 An Olympian is spinning in order to toss
a hammer in the hammer throw event. If the net force on the hammer remains perpendicular to the hammer’s motion, then the hammer’s
A. Mass will begin to change
B. Speed with begin to change C. Speed will remain unchanged.
Question 2 of 6
17
A telecommunications satellite is
placed in orbit around Earth at a
speed of 8 km/s. Earth’s gravity
exerts a perpendicular pull on the
satellite. How does this affect the
satellite’s speed?
A. Its speed will remain the same. B. Its speed will slowly increase. C. Its speed will slowly decrease.
Question 6 of 6
18
For a satellite in orbit around a
planet, which of these is true? The
satellite is constantly changing
A. Speed B. Velocity C. Mass
Question 4 of 6
19 A satellite in orbit around Earth travels at a
constant speed of 28,000 km/hr. What can be said about the forces on the satellite?
A. Force must constantly act on the satellite
perpendicular to its direction of motion.
B. Force must constantly act on the satellite in
the direction of forward motion.
C. No net forces act on the satellite if the speed
is constant.
D. Force acts in the direction which is away from
How is Centripetal Force related
to Newton?
Acceleration is toward the center because
that’s the direction of the force…
Formula!
23 The formula used to calculate centripetal
acceleration is:
So what is the equation for Force?!
F is force, measured in Newtons (N)
m is mass, measured in kilograms (kg)
v is velocity, measured in m/s
r is radius, measured in meters (m)
I DO
An Olympic disc thrower spins a 5.00 kg
disc in a 0.5 meter radius at a speed of 8 m/s. What is the force being exerted on the disc?
WE DO
26 What is the radius of movement for a 2
WE DO
27 What is the velocity of a car with a mass
YOU DO: Physics Speed
Dating
28 You are about to take part in the 1st
annual Physics Speed Dating
Be respectful, be kind, don’t leave your
date hanging. You cannot date the same person twice
At each date, you don’t need to copy
down the question, just answer it together
At each date, you also need to find out
something interesting about your date (prompt will be given)
The Speed Dating
Date #1
29What is the force on a 60 kg cyclist as they make an 8 m radius turn at a velocity of 20 m/s?
Date # 2
30 Draw a quick picture of this and decide
where the centripetal is pointing and what is its source.
Date #3
31A toy car turns at a velocity of 1 m/s on a track with a radius of 4 m. If it took 10 N to make the toy car turn, what is the
mass of the car?
Date #4
32 Draw a quick picture of this and decide
where the centripetal force is pointing (draw it)
Date #5
33 What must be the acceleration of a car that is traveling at speed of 12 m/s to make a turn that is 5 m in radius? Which direction is the acceleration towards?
Date #6
34 What is the radius of a 4 kg paper
airplane that is spinning around at 5 m/s after 12.5 N was applied?
Date #7
35 What is the force on a 28 kg model air
plane traveling at a velocity of 3 m/s for a radius of 2 m?
Date #8
36 What is the centripetal force that keeps
the Earth orbiting the Sun?
Date #9
37 What must be the velocity of 65 kg
Spiderman spinning with a force of 585 N in a radius of 4 m?
