Unit 7: Circular Motion

Vote #1 Is the car accelerating?

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. 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? How does the cork accelerometer move (or not move) when you spin in a circle holding it? Are you accelerating? Are you accelerating?

Newton’s 1 st 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 Acceleration Slope 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 #2 Is the car accelerating?

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. 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

Centripetal Centripetal 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 centrifugal Round- up or gravitron

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 Law Tangent to the circle What would a motion map for this look like?

Twirling Stopper What variables might affect the force on the string? Period = Frequency = Rotations per second = Angular speed or rotational speed = Linear speed =

Formulas Centripetal Force Fc =Fc =Fc =Fc = Centripetal Acceleration ac =ac =ac =ac =

Unit 7: Circular Motion Examples

Centripetal Centripetal 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 Physics 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.