"Parachutes" Return to list of pracs

Aim: This activity is used to demonstrate how parachutes work.

Equipment: The equipment includes...  

• 1 large garbage bag;
• scissors;
• string;
• paper clips;
• plasticine.

Method: Cut up the garbage bag into small squares (about 30cm x 30cm work well). Tie 30cm lengths of string to the four corners and then tie them together to a single paper clip.

a. Why use a parachute? Make two parachutists out of identical amounts of plasticine and attach one to the parachute. Measure the time taken to drop each parachute from a height of about 2 metres. Drop the attached parachutist (attached to the parachute) and the unattached parachutist from 2 metres and compare "their injuries" to open a discussion of why we use parachutes.

b. Time of descent. What factors will affect the rate of descent? Change the design of your parachute to make 3 prototypes A, B and C and compare designs. Change the size of the parachute; the weight of the parachutist; the shape of the parachute (circle or square); etc. Record 3 times the time of descent. Find the average.

Parachute	Trial 1	Trial 2	Trial 3	Average
A
B
C

Background knowledge: Parachutes are used to increase the area exposed to air to increase drag. Blow on your hand. What do you feel? You feel air hitting your hand. There are billions of tiny particles hitting your hand continuously. Shape your hand so that you stop as much air as possible ... you are making the area of the hand as big as possible (ie. maximum surface area). A parachutist falling out of a plane, without  a parachute, gets close to 260km/h before reaching terminal velocity (the maximum speed possible where the force of gravity equals the force of air resistance ... the person no longer speeds up).

The number of air particles hitting a person falling (only) compared to hitting a person with a large parachute is very different. All those particles colliding with the parachute slow the parachutist down drammatically to a speed that makes landing possible without breaking a leg!