A Physics question...?

Question

Me and my friend have been wondering about this... soo, if you have a huge car, like an SUV, and a bowling ball, and you roll them both so they are both going at the same speed, which one will slow down first? One of us thinks it's the ball, cause it has less force pushing it, but the other thinks it's the SUV cause, being heavier, it has so much more friction. What do you think? My physics teacher might have told us, but we can't remember the answer... haha. Thanks!

Answer 1

The only thing that matters is the frictional forces compared to the mass. If they are on a very smooth, hard surface like a bowling lane, the ball has almost no air resistance or rolling resistance and would keep going longer. On grass, the ball would stop rather quickly and the SUV would keep rolling longer. I presume the SUV is in neutral with the brakes off.

Answer 2

It all depends on the effective friction coefficient. The bowling ball would likely go further because its rolling surface is hard and deflects little, thereby losing enrgy at a slow rate. The SUV has tires that flex under the weight and this flexing causes heat, which expends energy which comes out of the kinetic energy of the vehicle.

Once you let them go there's no 'push' except friction pushing opposite the velocity. If the coefficients of friction were the same, the SUV would have lots more retarding force, but a proportionately larger mass, so the decelleration would be the same. (a = F/m)

Answer 3

First of all, there is no force pushing either the bowling ball or the car if they started at a constant speed. There would be, however, a frictional force opposite the direction of motion that would slow these objects down. If I was to have to bet, I would pick the SUV to slow down first. A bowling ball is a fairly smooth object, to lessen friction between it and whatever surface it is on. In contrast, the rubber tires of the SUV are intentionally treaded to create extra friction for greater controlability and manuverability. This major difference in design should stop the SUV first and the bowling ball second. Mass and inerita are really irrelevant to this argument.

Answer 4

The thing about the friction though is that friction applies a torque making the wheels spin. The important fact is the direction of Friction. When a wheel of sphere roll along a flat surface, Friction is in the direction they are going. If you think about it, without friction they would not move but with friction they move, therefore there MUST be a force in that direction: friction. Therefore friction is practically irrelevant to this problem.

It involves Moment of inertia to a large degree. A rotating wheel has (.5)mv^2 Joules of energy used solely for making it rotate. Therefore the total energy of the moving SUV is (.5)M(total of wheels + SUV)v^2 + 4((.5)m(each wheel)v^2. The first part is normal non-rotating Kinetic energy of a moving mass and the second part is rotational energy used to make the wheels spin.

The rolling sphere has moment of inertia of (.4)MR^2. This means that a rolling sphere has (.5)mv^2 + (.2)mv^2 energy. Again the first part is standard kinetic energy and the second part is the energy required for its rotation.

Therefore, if one is to stop (though I am not sure I agree that across a level surface either will ever stop, provided the axles of the wheels of the SUV rotate frictionlessly) it would have to be the bowling ball first because it has less energy to start with. In fact even if the bowling ball had the same mass as the SUV, Due to it's lower moment of inertia, it would still stop first.

Answer 5

I think the bowling ball will stop first because it has less inertia and less mass so its easier to stop. But the friction force thing makes a good point too so the SUV might stop first.

wow thats a good question. im asking my physics teacher monday.