Activity B: Energy Get the Gizmo ready:
Click Reset, and check that One sled is selected.
Drag the red sled so that its height is 25.0 m.
Set the Red sled mass to 100 kg.
Introduction: Energy can be found in several forms. Kinetic energy is energy of motion. Potential energy is stored energy, such as the stored energy of a sled at the top of a hill.
Question: How are potential and kinetic energy related to one another?
Collect data: Turn on Show energy. Notice that energy is measured in joules (J). In the table, record the potential and kinetic energy of the sled at the top of the slope, about halfway down, and at the bottom. (Use the Pause button to stop the sled halfway down.)
Location Height Potential energy Kinetic energy Total energy
Top 25.0 m
Middle
Bottom 0.0 m
How do the potential and kinetic energy change as the sled moves down the slope?
Add the potential and kinetic energy for each location to find the total energy. What do you notice about the total energy? According to the law of conservation of energy, energy can be changed from one form to another, but it cannot be created or destroyed. That means that the total amount of energy at the beginning is the same as the total amount at the end.
Explore: Vary the sled’s height and mass. Observe the effect of each change on the potential energy of the sled.
How does potential energy change when height is increased?
How does potential energy change when mass is increased?
Compare a sled’s potential energy at 10 m to its potential energy at 20 m. How does doubling height affect potential energy?
Compare the potential energy of a 100-kg sled and a 200-kg sled at the same height. How does doubling mass affect potential energy?
Measure: Click Reset. Set the Red sled mass to 100 kg and the Snowmen to 1. Drag the sled to the top of the hill. Click Play and then Pause just before the sled hits the snowman.
What is the speed of the sled before it hits the snowman?
What is the kinetic energy of the sled before it hits the snowman?
Click Play. What is the speed and kinetic energy of the sled after hitting the snowman?
Speed:
Kinetic energy:
How much energy was used to destroy one snowman?
Predict: Click Reset. Drag the sled to a height of 40 meters and set its mass to 160 kg.
What is the potential energy of the sled?
How many snowmen do you think this sled can destroy? Explain your answer.
How many snowmen do you think this sled can destroy? Explain your answer.
Extension 1: The formula for potential energy is PE = m • g • h. In this formula, PE stands for potential energy (in joules), m stands for mass (in kilograms), h stands for height (in meters), and g stands for acceleration caused by gravity. On Earth’s surface, g is 9.8 m/s2. This means that, every second, the speed of a falling object increases by 9.8 m/s.
Calculate the potential energy of a 20-kg sled at 40 meters. ✏️Show your work in the space to the right. When you are done, use the Gizmo to check your answer.
Potential energy:
Extension 2: The formula for kinetic energy is KE = m • v2. In this formula, KE stands for kinetic energy (in joules), m stands for mass (in kilograms), and v2 stands for speed squared, or the speed multiplied by itself.
Calculate the kinetic energy of a 20-kg sled moving 28.0 m/s. ✏️Show your work in the space to the right. To check your answer, set the height to 40 m and the mass to 20 kg. Click Play and wait until the sled gets to the bottom.
Kinetic energy: