Shadows simulator

What this simulator shows

A shadow forms where an object blocks light from reaching a surface. Here a lamp shines on a block 14 cm tall that stands on a table in front of a wall. Drag the lamp, or use the Closer, Farther, Higher and Lower buttons, and the shadow is worked out from straight-line light rays. A dashed line shows the ray that just skims past the top of the block. The readout gives the shadow's length on the table and its height on the wall, and you can switch the block between opaque, translucent and transparent.

• Light travels in straight lines, so a shadow has the same outline as the object blocking the light.
• A higher lamp makes a shorter shadow on the table; a lower lamp makes a longer one.
• When the lamp is low, the shadow can reach the wall. A lamp close to the block makes a bigger shadow on the wall.
• Opaque objects make dark shadows, translucent ones pale shadows, and transparent ones almost none.

Why hands-on helps

Children see shadows every day but rarely change them on purpose. Moving the light source one step at a time, and seeing a number change, helps them notice patterns and explain them with the straight-line idea. It also connects to the Sun: shadows outside are long in the morning and evening, when the Sun is low, and short around midday.

Common misconceptions

Young children often think a shadow is something the object gives off, like a dark copy of itself. A shadow is simply a place light can't reach. Many expect shadows to always get bigger when the light gets closer. That is true for the shadow on the wall here, but on the table, moving the lamp closer from the side makes the shadow shorter. Another idea worth checking is that clear objects make no shadow at all; a clear glass block still makes a very faint one, because a little light is reflected and bent at its surfaces.

A 10-minute shadow activity

• Ask: "How could we make this shadow longer?" Let the child try their idea.
• Press Higher three times and read the table shadow each time. Then press Lower.
• Ask the child to describe the pattern in one sentence.
• Try the challenge to climb the wall at least 10 cm.
• Switch to translucent and transparent. Ask which materials at home would make each kind of shadow.

Where this fits in school

• US, grade 1: NGSS 1-PS4-3 asks students to test the effect of placing objects made of different materials in the path of a beam of light.
• US, grade 5: NGSS 5-ESS1-2 asks students to show patterns in the daily changes of shadow length and direction.
• England, Year 3: pupils learn that shadows form when light is blocked by an opaque object, and find patterns in how the size of shadows changes.
• England, Year 6: pupils use the idea that light travels in straight lines to explain why shadows have the same shape as the objects that cast them.

Learning more

Light and shadows are on Eurekami's science skill map, with lessons that draw the light rays live and talk them through. Daily practice adds a few quick science questions alongside math and English.