Centripetal acceleration
Race Cars with Constant Speed Around Curve When acceleration could involve a change in direction and not speed
⇐ Use this menu to view and help create subtitles for this video in many different languages.
You'll probably want to hide YouTube's captions if using these subtitles.
- So we have some, some race cars racing right here
- and I have an interesting question to ask you.
- If we assume that these cars
- are making this turn right over here,
- that all of them are making this turn
- at a constant speed.
- So a constant speed
- constant speed of 100 kilometers per hour.
- 100 kilometers per hour.
- My interesting question for you is,
- are these cars accelerating while they make this turn?
- So, is acceleration happening?
- Acceleration.
- And you might say
- Well, gee, look, my speed was constant, it's not changing
- if I look at this speedometer for the car here,
- If I look at this speedometer over here
- it won't budge, it just stays in a 100 kilometers per hour.
- I don't have any change in speed over time.
- And so then, you might say
- that you don't have any acceleration.
- But then you might be saying why would Sal
- even make this video, you know,
- why would that question even be interesting?
- And your second, your second suspicion would be true
- because these cars actually are accelerating.
- They actually are accelerating
- despite having a constant speed.
- And you can pause it and think about that
- for a second if you want to.
- But I wanted to point this out to you because
- in an example like this, the difference
- between speed and velocity starts to matter.
- Speed being a scalar quantity
- only having a magnitude
- and velocity being a vector quantity
- having speed with a direction
- having a magnitude and a direction.
- And to think about.
- Let's take a top view of this thing
- And I think It will become a little bit clearer
- the difference between speed and velocity
- and why these things are accelerating.
- So, if I were to take a top view of this race track.
- I'll do my best attempt to draw it.
- So, it might look something like this.
- This is the top view.
- I can even draw this red and white.
- So, red, just to give you the idea.
- So, this is the red
- and there is some white in between.
- I miss I'm not drawing as many dividers
- as there are in the actual picture
- but it gives you an idea of
- what I'm actually drawing.
- And there's some grass out here,
- there's some grass over here,
- and there is some grass over here.
- And let's focus on this orange car,
- this red car over here.
- So, (where?) you say..
- And this is a top view.
- This is it's path right over here.
- (We're?) saying it has a constant speed
- of a 100 kilometers per hour.
- So if you think about its velocity.
- If you think about its velocity,
- the magnitude of its velocity is constant.
- It is a 100 kilometers per hour.
- But what is happening to the direction
- of the velocity, remember velocity is a vector quantity.
- It has magnitude and direction.
- So, up here, at this, where it's starting to enter the curve
- it's going in this direction.
- And you, (tend?) to show vectors by arrows like this,
- (and what you do is?) the arrow is going in the direction
- of the velocity in this case, and (normally?) you draw
- the length of the arrow shows what is the velocity,
- the magnitude of the velocity, I should say.
- So, its velocity is constant, so the length of this arrow
- will always be constant, but as we see
- it's direction changes, when it's halfway through the turn
- it's not going in the same direction.
- It is now going in the different direction,
- and when it comes to the bottom of the turn
- it's going in the very different direction.
- And it'll keep, the direction keeps changing
- as long as it is turning.
- And I'm not gonna go into math here, we're gonna wait
- for the math on this a little bit later,
- but remember
- acceleration is a change in velocity over time.
- Acceleration is equal to a change in velocity
- is equal to a change in velocity
- over time, or we could say, over change,
- over a change in time.
- And although the velocity's magnitude is constant here
- its direction is changing
- it keeps being...
- if there's no acceleration on it
- it's magnitude and the direction of it's velocity
- would be constant.
- And the car would just keep going, would just keep going
- in that direction.
- So, somehow the car is, the car's direction
- is changing inward, over and over and over again.
- And (...) this is kind of a little bit trick question,
- something for you to think about,
- we're gonna to discuss the math in more detail
- in future videos.
- But what's happening here is the,
- the car is actually (are) accelerating.
- And they're actually accelerating inwards,
- and that's what's changing inwards.
- We wanna say inwards.
- They're being accalerated towards the center of the curve.
- They're being accelerated to the center of the curve.
- And that's what's allowing their direction
- to actually change.
Be specific, and indicate a time in the video:
At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
|
Have something that's not a question about this content? |
This discussion area is not meant for answering homework questions.
Discuss the site
For general discussions about Khan Academy, visit our Reddit discussion page.
Flag inappropriate posts
Here are posts to avoid making. If you do encounter them, flag them for attention from our Guardians.
abuse
- disrespectful or offensive
- an advertisement
not helpful
- low quality
- not about the video topic
- soliciting votes or seeking badges
- a homework question
- a duplicate answer
- repeatedly making the same post
wrong category
- a tip or feedback in Questions
- a question in Tips & Feedback
- an answer that should be its own question
about the site
Share a tip
Suggest a fix
Have something that's not a tip or feedback about this content?
This discussion area is not meant for answering homework questions.