Quick answer: Kinetic energy is the energy an object has because it is moving, and it grows with both mass and speed. This grade 7 science lab on kinetic energy gives the aim, the equipment, the safety points, a step-by-step method, sample results and 8 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
How does the height from which a ball is released change how far it can push a cup? This lab links release height, gravitational potential energy and kinetic energy, using only a ramp, a ball bearing and a ruler.
Level: Grade 7 science (Year 8 · Class 7) · Curriculum: MS-PS3-1, MS-PS3-2
Aim
To find how the release height of a rolling ball affects how far it pushes a plastic cup, and so how its energy changes.
Equipment
- A grooved ramp (a plastic curtain rail or a folded card) and two or three books
- A steel ball bearing of mass 16 g (0.016 kg)
- A lightweight plastic cup lying on its side
- A metre rule and a marker pen
Safety
Place the ramp away from the table edge and keep feet clear so no rolling ball can hit you. Pick up any ball that rolls onto the floor straight away so nobody slips on it.
Method
- Prop the ramp on books so it makes a gentle slope. Place the cup on its side at the bottom, with its open end facing the ramp.
- Release the ball from a height of 5 cm above the table. Measure how far the cup slides and record it.
- Repeat three times at each height and calculate the mean.
- Repeat for heights of 10, 15, 20 and 25 cm. Reset the cup each time.
Results
Sample measurements from one group are shown below.
| Release height (cm) | Push 1 (cm) | Push 2 (cm) | Push 3 (cm) | Mean push (cm) |
|---|---|---|---|---|
| 5 | 1.7 | 1.9 | 1.8 | 1.8 |
| 10 | 3.8 | 4.1 | 3.8 | 3.9 |
| 15 | 6.0 | 6.3 | 6.0 | 6.1 |
| 20 | 7.6 | 8.0 | 7.8 | 7.8 |
| 25 | 10.0 | 10.4 | 10.2 | 10.2 |
Analysis questions
Question 1 Variables
1. State the independent variable.2. State the dependent variable.
3. Name two variables that must be kept the same.
Question 2 Energy at the top
Calculate the gravitational potential energy of the ball at each release height in millijoules (mJ). Use g = 9.8 N/kg. 1 J = 1000 mJ.Question 3 Draw the graph
Plot a graph of mean push distance (y-axis) against release height (x-axis). Draw a straight line of best fit through the origin and describe the pattern.Question 4 Gradient
Use the point (25 cm, 10.2 cm) to calculate the gradient of the line. State what it means.Question 5 Prediction
Predict the push distance for a release height of 30 cm and say how reliable the prediction is.Question 6 Why distance shows energy
Explain why the push distance can be used to compare the kinetic energy of the ball at the bottom.Question 7 Energy losses
The ball cannot transfer all its original gravitational potential energy to the cup. Suggest two reasons.Question 8 Improving the lab
Look at the spread of the three pushes at 25 cm. State the range and suggest one improvement.
