Bell Work: Acceleration Review What are the three ways to accelerate. Give an example of something speeding up. Give an example of something slowing down. Give an example of something turning. What is required to make something accelerate?

Circular Motion When an object rotates around an axis, it rotates around its center of gravity. Think of at least 5 Examples: satellite in orbit, car around a curve, ice skater spinning, backflip

Revolution – once around the circle Distance of 1 revolution is circle’s circumference Time of 1 revolution called period (T) ac is always perpendicular to the velocity

Knowledge Check! A. In what direction does a rotating object accelerate? Towards the center of the circle B. What do you remember about the direction of the net force and the acceleration? They are in the same direction C. So what direction does the net force act??

r = radius in meters T = time in seconds We will study objects only moving at a constant speed in circle. What is the equation for constant speed? r = radius in meters T = time in seconds Tangential velocity is the constant speed of rotation in a direction tangent to the circle

Self Quiz D. When is the speedometer reading in your car a tangential velocity? When you are going around a curve E. How does it feel when you go around a curve really fast? Like you are being thrown to the outside of the curve.

Merry-go-round: You move faster on the edge than in middle because radius is larger on the edge. Rotational velocity measured in RPM Revolutions per minute Ex: car engine, records

Centripetal Acceleration Acceleration occurs because the velocity’s direction is changing. Called centripetal acceleration (ac). Acceleration is always towards the center of the circle.

F. What is your favorite circular ride at the amusement park. Why. G F. What is your favorite circular ride at the amusement park? Why? G. How many circles does it have? Describe each to your neighbor. H. Why do you “feel” like you are being pulled away from the center? Your inertia makes your body want to move in a straight line tangent to the circle, which is away from the center. I. In what direction are you actually being accelerated? Toward the center!

A net force is needed to cause acceleration Called centripetal force (Fc) Force always toward the center of circle. Examples: dryer – metal tub pushes on clothes toward center, water escapes through holes Car around curve – friction or the bank (tilt) of the road pushes car toward center

What exerts the centripetal force? Track star rounding a corner. Airplane banking. Swing ride at six flags. Ceiling fan. Dog chasing tail. DVD spinning. Intermolecular forces

Conclusion If force is eliminated, zero /acceleration occurs and the object moves off in a straight line tangent (or perpendicular) to the circle because it has inertia.