Quick answer: A shadow forms when an opaque object blocks straight-line light. This grade 6 science lab on moon phases gives the aim, the equipment, the safety points, a step-by-step method, sample results and 7 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
How does the size of a shadow depend on the distance between an object and the lamp? In this lab you measure the shadow of a card at five distances, analyse the pattern, and then use a ball and a lamp to model the phases of the Moon.
Level: Grade 6 science (Year 7 · Class 6) · Curriculum: MS-ESS1-1
Aim
To find how the height of a shadow changes when an object is moved away from a lamp, and to model the Moon’s phases with a ball and a lamp.
Equipment
- Small bright lamp or torch
- Card 10 cm tall, fixed upright with sticky tack
- White screen (paper on a book)
- Metre ruler
- Polystyrene ball on a pencil
Safety
A lamp can get hot, so do not touch the bulb and keep leads away from water. Never look straight into the lamp or at the Sun during the Moon-phase model.
Method
- Place the lamp at one end of the ruler and the screen at the 100 cm mark in a dim room.
- Stand the card so that its distance d from the lamp is 20 cm. Measure the height of the shadow on the screen.
- Repeat for d = 30, 40, 50 and 60 cm.
- For the Moon model, hold the ball at arm’s length and turn slowly on the spot with the lamp on one side. Note how much of the lit side you see in four positions: ball between you and the lamp, lamp at your side, lamp behind you, lamp at your other side.
Results
| Distance d (cm) | Shadow height (cm) | Shadow ÷ card height | Shadow × d |
|---|---|---|---|
| 20 | 50.5 | to calculate | to calculate |
| 30 | 33.8 | to calculate | to calculate |
| 40 | 25.2 | to calculate | to calculate |
| 50 | 19.8 | to calculate | to calculate |
| 60 | 16.9 | to calculate | to calculate |
Analysis questions
Question 1 Predict the shadow
Use shadow height = card height × 100 ÷ d to predict the shadow for d = 40 cm and compare with the measurement.Question 2 Trend
Describe how the shadow height changes as d increases.Question 3 Magnification
Calculate shadow ÷ card height for d = 20 cm and d = 60 cm.Question 4 A constant product
Calculate shadow height × d for each row and explain what you notice.Question 5 Moon model
For the four positions of the ball, state which phase each represents.Question 6 Sources of error
Suggest two reasons why the measurements are not perfect.Question 7 Improvement
Suggest one way to make the shadow edges sharper.
