Race cars with constant speed around curve | Physics | Khan Academy

When acceleration could involve a change in direction and not speed. Created by Sal Khan.

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[qbrt]

@mohalfur as a driver, I do autocross, there are three stages to a turn, turn in, mid-turn and exit, and you are not doing the same thing with the car at anyone point. Just before turn in you will have slowed to the speed necessary to make the turn, at turn in you are coasting, as you get to mid turn you are accelerating to keep a constant velocity and the tires just inside the edge of adhesion, and at turn exit you are accelerating as hard as possible. Hope that helps.

[mohammedalkhaled]

conclusion: acceleration is produced by changing in velocity's magnitude or its direction or both at the same time

[laguirre]

THANKS FOR THE TIME AND EFFORT FOR US ALL. my kids and i benefit!

[griftorifto]

@engmustafa83 Good point but that would relate to angular velocity. "The rate of change of angle with respect to time" Acceleration refers to the rate of change of linear velocity. The car is moving along a tangent to the curve at any point during the turn. Therefore the direction(tangential velocity) is changing and so is it's acceleration.
Hope I helped.

[jbrawley]

Do you have a lecture on banked curves? Your videos are extremely helpful especially when reviewing before tests, but this is one thing that I'm not great at and I couldn't find a video on it.

[mohalfur]

@qbrt Thnx a lot! Great that its coming from a driver.

[vrdesk]

Sal, please make more hedge fund videos, especially focusing on the startup and mangerial jobs.

[paziipa]

Thanks for making learning physics fun once again!

[bbmaj]

@khanacademy
Wasn't trying to make any point, I was just trying to make fun of hypothetical physics. Most of the scenarios are so absurd. I remember in High School calculating the thermal expansion of a continuous ring of steel that was around the earth's equator, to establish how high above the surface it would be if it raised the tempreature of the steel raised by 1C.

[octobermaxington]

@b0b0maj0 it's tricky because we non-physicists use acceleration to mean "speed up" but physicists use it to mean "change speed and/or direction" which I guess is what the video is getting at. So they aren't pressing down on the accelerator (I hope!) but they are experiencing the physical force of acceleration, which is what makes your body lean outward as you go around a curve (I think)

[ShrikantSinghYadav]

Please tell me about the Laws of Physics applies When Doing Bike wheelie.

[griftorifto]

@engmustafa83 Lets say It turns on a fixed diameter. The car is turning, but at each point during the turn he is heading in a straight line. The car's turn is made up of thousands of dif directions of where it faces at each second during the turn. Therefore if its direction is changing so is its velocity and its acceleration.

[dannyboy]

classical dynamics is good for the soul

[octobermaxington]

I first thought they weren't accelerating but then I thought about how when you go around a curve your body gets jerked around. If acceleration wasn't occurring, you wouldn't get jerked around. Is that a useful insight?

[enoughofengineering]

So this is about the different between speed and velocity.

[Jose-Sousa]

A way of explaining it, would be to decompose the velocity and acceleration vectors in their axis components and make some graphs about it :P

It funny how speed and velocity often mean the same thing when used in other contexts.

[Icyveins]

The problem you describe is a lot more complicated than that. And you don't reduce acceleration by slowing down, you reduce velocity. But the scenario of a car going around a sharp turn involves torques twisting the body(literally trying to flip the moving body over) in addition to centripetal acceleration. There's a large collection of partial differential equations which give you the total solution, but understanding all of it at once is even beyond me and probably Sal currently.

[Shoyrou]

@b0b0maj0 vector acceleration does not change the speed if it is perpendicular to the movement, simply changes the direction of the vector velocity. Sal will probably explain this using the Work equation. Wait for it, you will understand it quite easily.

[khanacademy]

@b0b0maj0 He's not increasing his speed. He could have already slowed down to 100 km/h for the turn and held it there for the turn.

[mohalfur]

@khanacademy
If you want the car to have the best possible traction around a curve, should you:
1. accelerate, 2.deaccelerate or 3. keep a constant speed through the turn?

Please Sal answer (Me and my friend are having a big discussion)