# Tag Info

Accepted

### Newton's third law cancelling

I'd really appreciate if someone could give a more descriptive answer on why Newtons Third Law does not cancel out. The effect of the forces each object exerts upon the other depends on the ...

### Newton's third law cancelling

Let me describe a setup that makes friction effect way smaller than exerted force: There is a demonstration apparatus called 'air table' It consists of a plate with small holes in it, spaced closely ...

### Newton's third law cancelling

You accelerate less than the ball does partly because of the frictional force (as you noted) but also partly because (in most cases) your mass is greater than the ball's, so the same force produces ...

### Newton's third law cancelling

All Newton's 3rd law is really saying is that every force is two sided. Forces don't act like this $\longrightarrow$ they act like this $\longleftrightarrow$ Or this $\longrightarrow \longleftarrow$ ...
Accepted

### Is the system of parallel springs always have a same extensions?

Yes; a resultant torque causes rotation. If you don’t see this addressed in a problem, it’s because the block is being assumed to translate only, not rotate (e.g., perhaps it’s riding on frictionless ...

### Force needed to hold a book between your hands - not sure about the influence of friction

The frictional force is the only force in this situation that opposes the weight of the book. The hands in this case are providing the normal force that you will recognize from an inclined plane ...
1 vote

### What forces act on an element taken in a body which is subjected to no external forces?

For the simple geometry of the block, any small volume element has a downward force due to the mass above it. This force acts on the top surface of the volume. On the other hand, its bottom surface ...
1 vote

### What forces act on an element taken in a body which is subjected to no external forces?

At a molecular level there are attractive forces between the molecules of any solid - this is what stops the molecules on the surface of the object just drifting away, and so lets the object retain ...

### Conservation of energy in a rigid body

Yes, there are internal forces that hold the rod together. If there were no internal forces (imagine if the rod suddenly turned into sand), every piece of the rod would simply fall straight down.
Accepted

### Elemental problem of dynamics

Let M be the mass on the flat surface and m be the mass hanging. Assume equilibrium. The force balance on m is $$(1)T = mg$$ The horizontal force balance on M is $$(2)F_f = T$$ where (3)F_f = \...

### Friction when a car is moving in a circle

First of all, there are problems with the figures. The centripetal force always acts towards the center of the circular motion. The centripetal force and the static friction force shown in the ...
1 vote

### Friction when a car is moving in a circle

There is a static friction force from the road acting on the bottom of each tire. One component of this provides the centripetal force (and centripetal acceleration) toward the center of a circular ...
Accepted

### Force required to move a liquid through a specified opening

The key phrase you want to search on is fluid flow through an orifice. It isn't simple. In addition to the parameters you gave, it depends on at least the following: The shape of the orifice, in ...

### What rotates a disk hung at center of mass when it is tilted?

Most methods of attachment bend the string when you tilt the plate at the point where the string connects to the plate. Strings under tension want to be straight. Along with non-zero plate thickness ...

### Free-body-diagram of a falling ball

For a sphere drag force = 6πnrv (stokes' law) {v=velocity} so in start v=0 so drag =0 so net force is downwards so as ball comes down net force is downwards so velocity of increases in downward ...
1 vote

### Free-body-diagram of a falling ball

I don't understand how you concluded that the ball is slowing down. It isn't. Its acceleration is decreasing. If it were slowing down, the velocity-time graph would curve downwards. Here it is ...

### Simple forces diagram of a car maintaining speed up a slope

At the level you are asking about the system that you are considering (the car) should be treated as a point mass at the centre of mass of the car. After all in a real car there are two (four) normal ...
1 vote

### Simple forces diagram of a car maintaining speed up a slope

I like the second diagram. The downward force is the weight of the car (from gravity). (That can be broken into components; one backwards and one perpendicular to the road. The normal force (up and ...