A lab based introduction Circular motion A lab based introduction
Key vocab Revolving: moving in a circle around something Earth around the sun Rotating: Spinning around an axis The earth spins every 24 hours
Key vocab pt 2 Time: how long something takes to happen. (s) Period: how long something takes to happen once. A reoccurring event. (s) Frequency: how many times per second something happens. (1/s) or (hz)
Period, frequency or time? A moving around the classroom game What is it? Period, frequency or time? A moving around the classroom game
It takes 3 hours to run a marathon It takes about a minute to run each lap during a mile run An engine idles at around 1000 rpm
The earth rotates 1 time per 24 hours Same game The earth rotates 1 time per 24 hours The earth takes 24 hours to complete a rotation The earth rotated for 24 hours
Vocab. What is velocity?
*Disco ball spot activity* Vocab *Disco ball spot activity*
Big picture For an object moving in circles… Velocity=d/t V=2πr/T T means period (s) V=2πr*f f means frequency (1/s)
Forces involved in circular motion! …What does a force do again? What is acceleration? What is the unit of force? …if a object moving in a circle is moving at a constant rate is there even a force involved?
Intro to lab *explain set up, data collection and materials involved*
Lab question 1 As you increase the mass on the center hanger what happens to the velocity of the rotating object. Graph at least 3 points. Do 2 trials per point. You have 10 minutes.
Lab question 1 If forces cause acceleration, what acceleration does this mass cause?’ Based on your graph which is more correct? F α V F α 1/V
Lab Question 2 As you increase the mass on the revolving mass, what happens to the speed it’s traveling at? Graph at least 3 points and do 2 trials per data point.
Lab question 2 As the spinning mass increases the without changing the force it will spin slower. The faster something spins the more force it requires to keep moving in the same circle. With this in mind which is more correct? Circular force α m*v^2 Circular force α v^2/m
Lab question 3 If something is falling at a constant rate it is still exerting a constant force. Spin your mass and then just hold still and allow the center mass to fall at a roughly constant rate. What happens to the velocity? Do the experiment several times. Graph what radius (y) versus velocity (x) looks like.
If the radius increasing results in a slower spin while force is constant then F α v^2/m
Summary From all your data we can combine these and we find F centripetal= mv^2/r
That centripetal thing… Centrifugal force is not a thing. it comes from inertia. Centripetal force keeps things going in circles. It’s directed towards the center of the circle.