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Potential and Kinetic Energy Lab

Instructor: Amanda Robb
In this lab, we'll be studying the principle of conservation of energy. We'll use a ball to measure potential energy and kinetic energy and examine how the energy is converted from one form to another as the ball falls from a high place.

Introduction

Goal: Investigate conservation of energy through measuring potential and kinetic energy
Age: High school and up
Safety Concerns: None
Time: 1 hour

Think about what you already know about energy. You're probably considering the lights in your home or maybe the fuel you need to run a race. You wouldn't be wrong, but every object, moving or stationary, has energy. Each object can only have a certain amount of energy and that energy is in different forms. Think of total energy like a pizza. You always get 8 slices, but some of those slices might be cheese, while others might be pepperoni. Energy is never created or destroyed, only converted between forms - this is known as the law of conservation of energy.

We'll study two main types of energy today. Kinetic energy (KE), the energy of movement, and gravitational potential energy (GPE), or stored energy due to height.

Let's practice our energy types. If a ball is sitting still at the top of a hill, will it have GPE or KE? Since it's still and high up, the object only has GPE. If that ball rolls down the hill however, all the GPE is converted to KE when it gets to the ground and is moving fast.

Conservation of energy
conservation of energy

Today, we're going to see how this plays out in the real world. You'll be measuring the GPE of a ball 4 meters off of the ground and comparing it to the measured KE right before it hits the ground. Before you start, make a prediction: Will the GPE at the top be the same as the KE at the bottom? Why or why not?

Materials

  • One tennis ball
  • Meter stick
  • Timer with milliseconds
  • Calculator
  • A notebook to record your data
  • Balance that measures mass

Steps

1. Measure the mass of your ball on the balance. Make sure you record the mass in kilograms in your notebook. If you measure it in grams, simply divide the number by 1000 to get kilograms.

2. Measure the height from which you'll be dropping your tennis ball. It should be least 4 meters so that you can measure the time easily. A stairwell or out a window work well.

3. Get your timer ready and prepare to drop the ball. You'll need to measure the time from when the ball leaves your hand to exactly when it hits the ground. Record your time in your data table in seconds.

4. Repeat step 2 three times and average the times together. This allows for a more accurate measurement. Record this in your notebook.

5. Next, we need to do some calculations to find GPE and KE. Let's start with GPE. The equation for GPE is mass multiplied by acceleration due to gravity, multiplied by height:

Acceleration due to gravity is always 9.8m/s2; however, it is acceptable to round this to 10m/s2 for easier calculating. So, multiply your value for height, the mass of the ball, and 10m/s2 to get GPE.


GPE formula
GPE formula


5. Now find KE. The equation for KE is 0.5 multiplied by mass, multiplied by velocity squared:


KE formula
KE formula


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