Post on 23-Dec-2015
Unit 7: Circular Motion
Vote #1Is the car accelerating?
http://www.clker.com/clipart-red-car-top-view-6.html
Cork/Jar Accelerometer
How does it move when you are accelerating?
How does it move when you have a constant velocity?
Why does it do this? Newton’s First Law • The water has more mass and therefore more inertia. It is
more difficult to change the motion of the water.
• How does the cork accelerometer move (or not move) when you spin in a circle holding it?
• Are you accelerating?
Newton’s 1st Law
“The Law of Inertia”
An object with constant velocity keeps constant velocity unless an unbalanced force acts on it.
Mass is a measure of the inertia of an object. More mass = more inertia.
Cork/Jar Accelerometer
How does it move when you are accelerating?
How does it move when you have a constant velocity?
Why does it do this? Newton’s First Law
The water has more mass and therefore more inertia. It is more difficult to change the motion of the water.
How does the cork accelerometer move (or not move) when you spin in a circle holding it?
Are you accelerating?
Physics Definitions
AccelerationSlope of velocity vs. time graph
The rate of change in velocity
a = ∆v/∆t
Velocity Slope of position vs. time graph
Speed with direction
v = ∆x/∆t
Vote #2Is the car accelerating?
http://www.clker.com/clipart-red-car-top-view-6.html
Newton’s Second Law
When an object is subjected to a constant unbalanced force it experiences an acceleration that is directly proportional to the unbalanced force and inversely proportional to the mass of the object. The direction of the acceleration is the same as the direction of the unbalanced force.
Centripetaladjective
moving or tending to move toward a center
from Latin centrum ‘center’ + -petus ‘seeking’
Center-seeking
CentripetalCentripetal acceleration – the acceleration that is involved with the change in direction of an object moving in a circle.
Centripetal acceleration is ALWAYS directed toward the center of a circle.
Centripetal force - The special name given to the total force (also called net force) when an object is moving in a circle.
Centripetal force is ALWAYS directed toward the center of the circle. Centripetal force is a special name given to the net or total force and will NEVER show up on a force diagram.
Centrifugal force
Moving or tending to move away from a center
from Latin centrum ‘center’ + -fugus ‘fleeing’
Center-fleeing force
Centrifugal force
Physics types put centrifugal force in the same category as the stork who brings babies!
It does not exist!
Centripetal vs centrifugalRound- up or gravitron
http://www.youtube.com/watch?v=x_FF4iqvTkA
www.youtube.com/watch?feature=fvwp&NR=1&v=tkt-w5SczJQ
https://www.youtube.com/watch?v=yMmtdP_5UJQ
Uniform circular motion
Uniform circular motion involves acceleration without a change in speed.
Twirl the stopper at a constant velocity.
If you let go of the string, what direction does the stopper move?
Straight line – Newton’s First LawTangent to the circle
What would a motion map for this look like?
Twirling StopperWhat variables might affect the force on the string?
Period =
Frequency =
Rotations per second =
Angular speed or rotational speed =
Linear speed =
Formulas Centripetal Force
Fc =
Centripetal Acceleration
ac =
Unit 7: Circular Motion
Examples
CentripetalCentripetal acceleration – the acceleration that is involved with the change in direction of an object moving in a circle.
Centripetal acceleration is ALWAYS directed toward the center of a circle.
Centripetal force - The special name given to the total force (also called net force) when an object is moving in a circle.
Centripetal force is ALWAYS directed toward the center of the circle. Centripetal force is a special name given to the net or total force and will NEVER show up on a force diagram.
Centrifugal forcePhysics types put centrifugal force in the same category as the stork who brings babies!
It does not exist!
A person in a rollercoaster car is traveling at 12.0 m/s over a hill with a radius of curvature of 15.0 m. Use the 5 step method to determine the magnitude of the normal force on a 75kg person. What happens to the size of the normal force as the car travels faster and faster?
Draw a schema and force diagram for a ball on a string being twirled in a vertical circle at the point when it is at the tippy top. Write equations for the sum of the forces in the x and y directions.
Draw a schema and a force diagram for a car going at a constant speed around a curve. Write equations for the sum of the forces in the x and y directions.
The rotor is an amusement park ride in which riders line up against the wall of a circular room. The room starts to spin and eventually the floor drops out. Draw a force diagram for a rider on this ride. Write equations for the sum of the forces in the x and y directions.