It cant be because of increased surface area or anything of that sort, because friction is independent of area of contact
2006-10-17 01:30:39 · 6 answers · asked by nandu 1 in Science & Mathematics ➔ Physics
As the wheels go around you are having to continually "do work" to compress the side walls of the tyres at the front of the wheels. This requires energy.
You don't get this energy back when they decompress at the back of the wheels.
PS you are partly right about the friction bit. Your friction losses will be at the axle bearing & uneffected by the tyres. This is the friction that you need to over come to move.
The friction to give you traction (i.e. to stop you skidding) is effected by the surface area. This is why they deflate tyres slightly to get a car that is stiuck in mud/sand out of the mud/sand. You are right that this tyre/road friction doesn't need to be overcome to allow you to cycle.
2006-10-17 01:38:28 · answer #1 · answered by Me 3 · 0⤊ 0⤋
I would guess that it is because you have an extra layer of friction. When the tires are full you have the tires meeting the road, and they roll pretty smoothly.
When they are flat you also have the rim and edge of the tire rolling on the center part (the part that usually is on the road). Not only is this more friction, being rubber-on-rubber, but it is unstable - it can wobble left and right, and skid. Since the diameters of the rim and the tire are different, the inner surface is constantly being dragged over the bottom of the tire.
This isn't described very well (I wish I could draw a picture), I hope you get the idea.
2006-10-17 09:10:43 · answer #2 · answered by sofarsogood 5 · 0⤊ 0⤋
You are right, the force of friction is not affected by the area of contact. So what makes it harder to ride the cycle? First, let's recall that the force of friction acting on the tyres is equal to the coefficient of friction multiplied by the force normal to the area of contact, i.e. F=uN. What changes when the tyres are punctured is the coefficient of friction between the punctured tyres and the road surface. The coefficient of friction becomes larger in magnitude. Since it is directly proportional to the force of friction, F, the force of friction likewise becomes larger.
2006-10-17 08:58:21 · answer #3 · answered by tul b 3 · 0⤊ 0⤋
Well, I know it is - but have never given it much thought until now!
Maybe it is because, when the tyre is flat, several things are happening - first of all the tyre is 'squidging' around on the rim with no central point on which to ride. Then, as you know from riding a bike, even with fully inflated tyres it is almost imposssible to keep in an _exactly_ straight line. When the tyre is inflated this is not noticed. But when it is flat, and weight is being transferred first to one side then to the other, the instantaneous point of contact will be on one or other rim edge, and with the flattened tyre moving around, too, the whole wheel is unstable. Furthermore, the effort of steering and pedalling will be much greater, since you no longer have a resilient, narrow, smooth surface in contact with the road.
2006-10-17 08:50:24 · answer #4 · answered by avian 5 · 0⤊ 0⤋
The tires have more surface area on the ground. That means more friction, which means it's harder to ride.
2006-10-17 08:38:47 · answer #5 · answered by JP 2 · 0⤊ 1⤋
when the wheel is full of pressure from inside the only friction acting upon it is rolling friction when the wheel is flat sliding friction also acts upon it and sliding friction is more than rolling friction so thats it. is urs punctured???
2006-10-17 08:41:08 · answer #6 · answered by Anonymous · 0⤊ 0⤋