runny4
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http://i-want-to-study-engineering.o...cycle_turning/
In the video which is green and on the right it says that the friction is in the same direction as acceleration but isn't friction always opposing motion?
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maggiehodgson
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(Original post by runny4)
http://i-want-to-study-engineering.o...cycle_turning/
In the video which is green and on the right it says that the friction is in the same direction as acceleration but isn't friction always opposing motion?
Do you ride a bike? I do. I think that if I was tilted over like that then the wheels would be wanting to push away from the centre of turn. So friction has to act the way it does to oppose the potential motion.That's my view from real life

Also I recently had a question about direction of friction and TSR members replied that even if you labelled you diagram with F the other way you would get a negative value showing you which way it does act.

However, I'm no expert so perhaps you'll get someone who can give you a more mathematical explanation.
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nerak99
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If there were no friction, the bicycle world continue moving at the same speed in a straight line. However, it is changing direction and therefore there is a force (which in this case is the friction).

In other words, the friction is opposing the motion because without it, the mass world continue to move in a straight line.

When acted upon by a force a mass accelerates in the direction of the force. This is why the acceleration is in the same direction as the friction.

Since the force persists, the acceleration persists. This is where the idea comes from that in circular motion, the acceleration and force are directed towards the centre.

You now have to equate the central acceleration with the force using F=ma.
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runny4
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(Original post by nerak99)
If there were no friction, the bicycle world continue moving at the same speed in a straight line. However, it is changing direction and therefore there is a force (which in this case is the friction).

In other words, the friction is opposing the motion because without it, the mass world continue to move in a straight line.

When acted upon by a force a mass accelerates in the direction of the force. This is why the acceleration is in the same direction as the friction.

Since the force persists, the acceleration persists. This is where the idea comes from that in circular motion, the acceleration and force are directed towards the centre.

You now have to equate the central acceleration with the force using F=ma.
When acted upon by a force a mass accelerates in the direction of the force. This is why the acceleration is in the same direction as the friction.

but it is moving at constant speed and why is friction in the same direction as acceleration in this case?
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nerak99
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Sorry about delay in responding.

The speed is not the issue, the velocity is and that is always changing (in this case).

Imagine you are on a bicycle going into a roundabout and your braces got caught on a car door handle and the car takes of round the roundabout all the way round whilst you wanted to go straight on. Your speed might be constant all the way round but your velocity is changing (i.e. there is an acceleration) because of the force created by the tension in your braces.

The force is towards the centre of the roundabout as is the acceleration.
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runny4
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(Original post by nerak99)
Sorry about delay in responding.

The speed is not the issue, the velocity is and that is always changing (in this case).

Imagine you are on a bicycle going into a roundabout and your braces got caught on a car door handle and the car takes of round the roundabout all the way round whilst you wanted to go straight on. Your speed might be constant all the way round but your velocity is changing (i.e. there is an acceleration) because of the force created by the tension in your braces.

The force is towards the centre of the roundabout as is the acceleration.
thanks
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