## LESSONS: Circular Motion

###### Centripetal Acceleration and Tangential Velocity

What is the relationship between centripetal ACCELERATION and tangential VELOCITY?

Try This

Using the Accelerometer tool, hold the mobile device outward at arm's length and pirouette or spin as uniformly as possible. Determine the direction of the net acceleration on the mobile device. Explain why this makes sense. Determine the qualitative relationship between velocity and net acceleration. Calculate the tangential velocity of the mobile device during the spin using a meter stick to measure your arm length. Estimate total net force after measuring the mass of your device with a balance.

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###### Locating an Accelerometer with Circular Motion

Where is the ACCELEROMETER located in my smartphone?

Try This

Measure the centripetal acceleration on a smartphone using the Accelerometer tool when placed on a record player moving at a constant speed. Determine the location of the accelerometer from the acceleration reading and the radius, measured with a meter stick.

Challenge Yourself

• How would the experiment be different if the speed of the record player was uniformaly faster or slower? Explain.

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###### Potential and Kinetic Energy of a Pendulum

What is the relationship between POTENTIAL ENERGY and KINETIC ENERGY of a simple pendulum?

Try This

Using the Accelerometer tool, fix the smartphone to the end of a simple pendulum made from a string attached to a point. Before releasing the pendulum from a given height (measured from the bottom of the pendulum swing), determine the potential energy using the mass of the smartphone and a ruler. Release the smartphone. Using data from the acceleration when at the lowest point, determine the tangential velocity at the lowest point (and hence, the kinetic energy).

Challenge Yourself

• How did the starting potential energy at the top of the swing compare to the kinetic energy at the bottom of the swing?

• How would this relationship differ if potential energy had been measured from the ground, and not from the bottom of the pendulum swing? Why?

• Draw energy pie charts for systems in which potential energy is measured from both frames of reference.

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###### Amusement Park Physics

Amusement Park Ride Analysis

Try This

Use the Accelerometer, Barometer, and/or Roller Coaster tools to investigate G-forces, acceleration, and circular motion on a variety of amusement park rides.

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