A toy parachute
Hang a 20 g, 50 g or 100 g toy under a canopy of 0.1 to 1 m², and find how fast it falls once air drag balances its weight, and how long it takes to drop 10 m.
Core concept
A falling object speeds up until air drag equals its weight; then it falls at a steady (terminal) speed v = √(2mg ÷ (ρCA)), so a bigger canopy falls slower
Topic: Science around us
When you drop a toy, gravity: The pull that makes things fall towards the Earth. All key words pulls it down with its weight: The pull of gravity on something, measured in newtons. It is less on the Moon. All key words, mg. As it speeds up, the air pushes back harder: air drag grows with the square of the speed: How far something travels in a certain time, like kilometres per hour. All key words and with the area facing the air. Soon drag equals the weight, the force: A push or a pull. Forces can start, stop or turn things. All key words balance, and the toy stops speeding up. It then falls at a steady speed called the terminal speed: v = √(2mg ÷ (ρ C A)), where ρ is the density: How much mass is packed into a space. Things less dense than water float. All key words of air (1.2 kg/m³), C is the drag coefficient of a canopy (about 1.5) and A is its area. A parachute works by giving a large A: four times the area halves the speed, and a gentle landing needs a low speed.
What you will learn
- Explain why a falling object reaches a steady speed.
- Find the terminal speed from mass and canopy area.
- Predict how area and mass change the falling speed.
Before you start
- Know weight = mg and that balanced forces give a steady speed.
Materials
- A plastic bag or handkerchief, thread, tape and a small toy
- A stopwatch (a phone is fine)
Equipment
- A safe place to drop from, such as a staircase, with an adult
Procedure
- Record a 50 g toy under a 0.25 m² canopy.
- Change the canopy to 1 m², then 0.1 m², and record.
- Hang a 100 g toy under the 1 m² canopy and record.
How this simulation is simplified
- Air density ρ = 1.2 kg/m³, drag coefficient of the canopy C = 1.5, g = 9.8 m/s².
- The toy has reached its steady speed for the whole 10 m (in real life it takes a short distance to get there).