# Tag Info

Accepted

### Why is it possible to keep an object, say a book, horizontal while holding its corner?

Since contact forces act on the axis of rotation, they don't exert any torque. mg would exert a torque unless the book's center of gravity is directly above or below the "hinge". You are ...
• 11.5k

### Why are angles so weird?

Your concerns are valid, and for that reason, there is also an alternative way to view angular velocities, angular momentums, etc.: They are not vectors, but bivectors. A bivector is essentially an ...
• 2,393

### Is Earth really flattened at the poles because of centrifugal force?

The description from an interial frame is that the bits of the Earth at the equator are moving faster than those near the poles, so they have more kinetic energy, and thus they are a bit farther away ...
• 28k
Accepted

• 38k

### Is Earth really flattened at the poles because of centrifugal force?

Centrifugal acceleration is a real acceleration. It is an acceleration term which appears when converting Netwon's laws of motion from an inertial frame into a rotating one -- the difference between ...
• 46.6k

### Will spinning a bullet really fast without changing its linear velocity make it do more damage?

For comparison, the translational KE of the bullet you describe is about 2500 J while the rotational KE is about 278 J when rotating at $10^6$ rpm (assuming a 9 mm diameter and treating the bullet as ...
• 48.3k

### Spinning gyroscope loses weight?

One thought as to why you might see this: Is your gyroscope perfectly balanced? If not, it will generate up and down forces as it spins. At one instant, it will press down harder on the scale and be ...
• 37.7k

### Spinning gyroscope loses weight?

A lot of people have been misled by this apparent effect, notably Eric Laithwaite in his later years1. I suggest that you need to be able to collect six-axis data at the point of contact, ...

• 1,947