# Tag Info

Accepted

### Confusion in kinetic and static friction difference and approaching problems

I don't know how to know when to apply kinetic friction and when to apply static friction If two objects are moving relative to one another (which they are here, since the blocks are sliding down the ...
• 57.5k

### Why is the work done by a force on a rigid body zero if the displacement of point of application of force is zero?

The work done by a force refers to the displacement vector of the application point of that force: you cannot arbitrarily change it. So it is wrong to use the displacement vector of the center of mass....
• 75.5k

### Stacked block problem & static friction

My understanding is that the only friction source is between the two blocks, gravity is included, and there is a friction coefficient $\mu$. I think your confusion is about how to put forces on a free ...
• 737

### Stacked block problem & static friction

I mean that in physics it’s taught that static friction is always equal and opposite to the applied force, so that the body can’t move due to friction. You need to be careful in identifying the "...
• 75.6k

### Confusion in kinetic and static friction difference and approaching problems

Simple answer: for static friction, people tend to loosely say, "$f = \mu N$" but what they really mean is "$|f| <= \mu N$". You don't necessarily know what the force of static ...
• 737

### Why does a rolling ball slow down?

The ball slows down due to rolling resistance. That resistance equals the normal force times the coefficient of rolling resistance. Rolling resistance occurs due to inelastic deformation of the ball ...
• 75.6k

### Two different friction coefficients. How contribute?

Static friction is similar to the reaction force that keeps the object from sinking through the table. Gravity pushes the object down, and the table pushes up with a force just strong enough to keep ...
• 42.5k

### Why does a rolling ball slow down?

When a ball or other object is sitting still, the normal force does pass through the center of mass. You can see this must be so from your diagram. If it did not, there would be a torque and the ball ...
• 42.5k
1 vote

### What is the Bike Speed vs. Wind Speed Equation?

About ten years ago, I wrote some computer code to do something like this. Unless the course is dead flat, you will want to account for elevation change too, because it will have significant effects ...
• 737
1 vote
Accepted

• 16.8k
1 vote
Accepted

### Minimum work done on a mass to take it along a path

If the particle begins and ends at rest, there is no change in kinetic energy which means the net work done by all external forces on the particle (gravity, friction and the applied force) is zero, ...
• 75.6k
1 vote

### Why is the work done by a force on a rigid body zero if the displacement of point of application of force is zero?

Why is the work done by a force on a rigid body is zero if the displacement of point of application of force is zero? Because in order for the force to do work on a body, the source of that force ...
• 75.6k

Only top scored, non community-wiki answers of a minimum length are eligible