You are Here: Home >< Physics

# Terminal velocity explanation?

Announcements Posted on
Last day to win £100 of Amazon vouchers - don't miss out! Take our quick survey to enter 24-10-2016
1. How does terminal velocity work, like the process?

This usually comes up as 6 markers
Feel free to use examples
2. (Original post by tamanna___)
How does terminal velocity work, like the process?

This usually comes up as 6 markers
Feel free to use examples
Normally, you are given the example of a sky diver:

1) As soon as the parachutist jumps, only weight acts, so no drag and they are accelerating downwards at the acceleration of freefall (9.81ms2). Resultant force is not zero, and it is downwards.

2) Later in the jump, they are still accelerating downwards but at an acceleration less than 9.81ms2 as drag is acting now. Weight > Drag so they still move downwards with a resultant force which is also downwards.

3) When they first open the parachute, the large surface area increases the drag force enourmously, so they accelerate upwards, with drag > weight, and resultant force now upwards.

4) A while after opening the parachute, the drag = weight which means they are at terminal velocity as the net force is 0, because the 2 forces are equal and they are travelling at a constant speed in the downward direction.

So, terminal velocity occurs when the drag force is equal to the weight, when the net force is 0 (no acceleration, constant velocity).

Any questions, feel free to ask
3. (Original post by derpz)
Normally, you are given the example of a sky diver:

1) As soon as the parachutist jumps, only weight acts, so no drag and they are accelerating downwards at the acceleration of freefall (9.81ms2). Resultant force is not zero, and it is downwards.

2) Later in the jump, they are still accelerating downwards but at an acceleration less than 9.81ms2 as drag is acting now. Weight > Drag so they still move downwards with a resultant force which is also downwards.

3) When they first open the parachute, the large surface area increases the drag force enourmously, so they accelerate upwards, with drag > weight, and resultant force now upwards.

4) A while after opening the parachute, the drag = weight which means they are at terminal velocity as the net force is 0, because the 2 forces are equal and they are travelling at a constant speed in the downward direction.

So, terminal velocity occurs when the drag force is equal to the weight, when the net force is 0 (no acceleration, constant velocity).

Any questions, feel free to ask
Thankyou! How would you explain it for a cyclist cycling? That question has come up once.. How would you start it off?☺️
4. (Original post by tamanna___)
Thankyou! How would you explain it for a cyclist cycling? That question has come up once.. How would you start it off?☺️
Is it a cyclist travelling horizontally, or downhill?
5. (Original post by derpz)
Is it a cyclist travelling horizontally, or downhill?
This is the question
Attachment 520297520299
Attachment 520297520299
Attached Images

6. (Original post by tamanna___)
This is the question
Attachment 520297520299
Attachment 520297520299
Im just unsure about what the drag force would be? Increase in wind or something?
7. (Original post by derpz)
Im just unsure about what the drag force would be? Increase in wind or something?
Air resistance is typically proportional to velocity (or at least modelled that way), so the faster you go the stronger the drag. Eventually, the drag = force from pedalling and you've hit terminal velocity.
8. Solve the DE for and take the limit as .
9. (Original post by Implication)
Air resistance is typically proportional to velocity (or at least modelled that way), so the faster you go the stronger the drag. Eventually, the drag = acceleration from pedalling and you've hit terminal velocity.
Yeah, I just never came across this example but this makes sense, so gradually, the acceleration would decrease until the air resistance is equal to the force provided by the pedals by the rider...correct?
10. (Original post by derpz)
Yeah, I just never came across this example but this makes sense, so gradually, the acceleration would decrease until the air resistance is equal to the force provided by the pedals by the rider...correct?
Exactly It would work the same way in the case of a skydiver before their parachute deploys - they still hit terminal velocity, it's just a much higher terminal velocity than without the parachute!
11. (Original post by derpz)
Yeah, I just never came across this example but this makes sense, so gradually, the acceleration would decrease until the air resistance is equal to the force provided by the pedals by the rider...correct?
You've worded it a bit weirdly but, essentially - yeah, the air resistance equals the driving force which then means no resultant and hence zero acceleration.
12. (Original post by Implication)
Exactly It would work the same way in the case of a skydiver before their parachute deploys - they still hit terminal velocity, it's just a much higher terminal velocity than without the parachute!
(Original post by Zacken)
You've worded it a bit weirdly but, essentially - yeah, the air resistance equals the driving force which then means no resultant and hence zero acceleration.
Got the hang of it, I was just unsure what the actual drag force would be. Thanks!
13. (Original post by Implication)
Air resistance is typically proportional to velocity (or at least modelled that way), so the faster you go the stronger the drag. Eventually, the drag = force from pedalling and you've hit terminal velocity.
(Original post by derpz)
Yeah, I just never came across this example but this makes sense, so gradually, the acceleration would decrease until the air resistance is equal to the force provided by the pedals by the rider...correct?
(Original post by Zacken)
You've worded it a bit weirdly but, essentially - yeah, the air resistance equals the driving force which then means no resultant and hence zero acceleration.
Thankyou all for helping!! I think i understand it better now

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: April 8, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

### Q&A with Paralympian Jack Rutter

Poll
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.