I constructed a parachute model and dropped it from a height of 3 meters. The tracker program shows that the parachute’s acceleration increases even after the parachute opens fully. For example, taking the downwards direction to be negative, acceleration at t = 1.00 s is -0.11, but acceleration at t = 3.00s is -0.97. I thought parachutes worked by decreasing the acceleration. How is my observation possible?

Any object will continue to accelerate until it reaches terminal velocity. Parachutes increase air resistance and, as such, lower the terminal velocity of an object. It is likely that your object has not reached terminal velocity and so is continuing to accelerate.

Expert Answers

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Parachutes work by increasing air resistance. When an object is falling, both gravity and air resistance act on it. If the force of gravity is greater, it will accelerate. However, this acceleration also leads to more air resistance. Eventually, the two forces balance out, and the object stops accelerating. This is referred to as terminal velocity. Without the intervention of outside forces, the velocity will remain the same, and acceleration will be 0.

When a parachute is deployed, the air resistance increases suddenly, and this causes the object to accelerate upward. This slows the object's speed and subsequently lowers its air resistance. As air resistance lessens, it will eventually balance with the gravitational force again. The object then reaches a new terminal velocity, which will be smaller than the initial terminal velocity without the parachute.

If you are dropping your model with the parachute already deployed, you will not see a change in acceleration. The object will continue to accelerate until it reaches terminal velocity. You could compare the velocity of the model with and without the parachute.

Additionally, 3 meters may not be a great enough height to allow the object to reach terminal velocity or observe a change in acceleration if you are deploying the parachute after the drop. Assuming that the acceleration values you've included are in m/s/s, these are relatively small values compared to acceleration due to gravity (without air resistance), which is 9.8 m/s/s. I think it's likely that your object is still accelerating because it has not reached terminal velocity.

For reference, it takes a skydiver 12 seconds of free fall (roughly 450 meters) to reach terminal velocity (Helmenstine 2020). If you have been tracking the velocity of your object as it falls, you can try to calculate its terminal velocity and see if you've reached it. I can't help you with that without more details on your model, but I've include a link that walks you through estimating terminal velocity.

I think the best course of action would be to make sure you're comparing acceleration before and after parachute deployment, and to drop your model from a much greater height. I hope this helps!

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