Science Buddies: "Ask an Expert"

hi there,

I must complete an experiment in grade 12 physics where i have to make a parachute that will successfully carry a tin of 280 mL of water down two floors to hit a target 3 m ahead (the target has a diameter of 60cm). It is a max/ min problem where we need to maximize flight time but minimize the weight of the parachute and the water lost. Please help me I am not sure how large the parachute has to be and what kind of material or shape works best. Also does it work better if we create a wiring inside the material so the parachute can catch the air easier? Thanks in advance!!

Hello natnatk,

Welcome to the forum. Your project sounds like a variation on the egg drop experiment. Except that you are trying to avoid spilling water instead of cracking eggs.

A successful parachute needs to produce enough drag to offset the weight of the payload. In your case the cup with 280 mL of water (the payload) weighs more than 280 g. The drag produced by the parachute varies with the parachute surface area. The parachute also must “fly” straight enough to hit your target. Well-placed holes in the parachute can help with this.

I found a parachute design for the egg drop experiment here:

http://www.aero.com/publications/parach ... keprch.htm

This parachute is made from a 30 inch diameter piece of plastic garbage bag. But this was used for an egg in a container with a combined weight of maybe half that of your cup of water. So, you need a parachute that is larger than 30 inches in diameter.

To find out the size you need you could conduct an experiment where you try parachute diameters larger than 30 inches. You could also try different shapes, for example rectangular. If you try a rectangular shape, you might start with dimensions that give you the same area as the circular one.

It is possible to estimate parachute design factors but the calculations are complicated. Here is a link that shows some example calculations for model rocket parachutes:

http://my.execpc.com/~culp/rockets/descent.html


I hope this helps and good luck with your project.

A. Norman