Recent content by BrainSalad

Thanks guys. Just a matter of confusion due to the specific application of the formula.

For a uniform, hollow cylinder, why is this derivation wrong? M = mass of whole solid cylinder m = mass of missing cylindrical piece R = radius of whole cylinder r = radius of missing cylindrical piece moment of inertia = moment of inertia of whole cylinder - moment of inertia of...

This makes good sense.

This doesn't explain the fact that a larger force is required to keep a spring stretched at greater length, does it? Two particles attracted to each other are still easier to pull apart when they are far away from each other, but a spring is opposite that.

Hooke's law states that the force required to stretch/compress a spring is proportional to the distance stretched. Meanwhile, electromagnetic interactions between particles obey an inverse-square law with respect to distance. So, if as a spring is stretched, it's composite particles get farther...

No work is done on the ice skater. NO internal forces can do work, because they transfer no energy from outside the system.

I like this idea, and have thought about it before, but it's wrong. The drive train does just as much positive work on the axle as the axle does negative work on the drive train, so no net work is done (equal, opposite forces exerted over same distance). This is the very reason that only...

No. It's a static friction force in the forward direction that drives the car forward. It could not accelerate from rest without that force, as per Newton's 1st law. A normal force always acts perpendicular to the surface.

Newton's laws would be a good place to start, my friend.

What's wrong with the premise? We can't take the whole universe as the object in question. You don't have any real physics education, do you? Every force is an internal force if you define the system large enough, but that isn't helpful a lot of the time.

Taking the car to be the system, the external force is the static friction force of the road on the tires. If you've really only learned about momentum the past two days, add to your knowledge that "external" and "internal" are relative terms. Any force exerted by an object outside the...

This is the way I thought about it originally. It's net momentum can't change without an outside force, but that has no bearing on the kinetic energy. An bomb for instance, converts chemical energy into kinetic and heat energy, without outside forces. The net momentum of all its exploded...

I think that depends on how the parts are interacting and which model you apply. Newtons 1st and 2nd, for instance, are valid for extended bodies and systems of particles as long as the velocities and accelerations considered are those of the COM. Work, however cannot be done without the...

I think he was referencing the skidding scenario, in which negative work is done on the car and the road and tires are heated up.

Before sophiecentaur casts this discussion into the depths of argument for no reason, thanks to everyone for the replies. I learned something.