# Tag Info

### What is the relation between rope length, object weight and force needed?

The human body is a terrible tool with which to understand Physics. It contains countless complications which turn simple equations into complex detailed patterns -- all in the name of being more ...
• 50.6k
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

### Two different versions of Newton's Third Law

... everybody has a different version of the law. No they don't. There is essentially only one version of Newton's Third Law, which is: If two bodies exert forces on each other, these forces have ...
• 57.5k

### 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 ...
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### Two different versions of Newton's Third Law

I think that you got the wrong idea about N3L as it is not to do with energy. In simple terms N3L states that the force on body $A$ due to body $B$, $\vec F_{\rm AB}$, is equal in magnitude and ...
• 98.6k

### 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 ...
• 797

### 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 "...
• 75.7k

### Does Newton's 3rd law hold true everytime?

No, the third law is alway valid, and it implies momentum conservation when there are no external forces. If you enlarge your system to include the objects that apply those external forces, then the ...
• 1,220
Accepted

### Does Newton's 3rd law hold true everytime?

Does Newton's 3rd law hold true everytime? The answer to the title of your post is no. While it holds for most forces, it does not in all cases. An example is magnetic forces. But it does hold for ...
• 75.7k

### Why does $W_1$ cancel out when $W_1$ perpendicular to the surface and Normal Force cancel out?

There is nothing dropping out. You are misunderstanding the physics that is being told to you.  \begin{align} \tag1\vec{\mathcal W}&=+\vec{\mathcal W_\perp}+\vec{\mathcal W_\parallel}\\ \tag2\...
1 vote

### Does Newton's 3rd law hold true everytime?

Newton's third law is just conservation of momentum in disguise. In the case where action-reaction pairs are net forces between bodies, we can say that conservation of momentum implies Newton's third ...
• 16.8k
1 vote

### How to calculate tension in this case?

Your example is statically indeterminate, meaning one of the strings is redundant (i.e. not required for the bar to be in equilibrium). This means the equations for static equilibrium alone are ...
• 75.7k
1 vote

### How to calculate tension in this case?

If your three strings are non-parallel you should be able to solve for the forces independently. But if they are all vertical or there are many more, then then you have discovered a topic called &...
• 797
1 vote

### I would like to calculate the lifting force required to stand up my motorcycle after laying it down on its side (real life scenario after a crash)

For me, it was a real life scenario after letting it fall over. Imagine the bike is laying on its side. One your friend is holding up the wheels and you are holding up the handlebars. Between the two ...
• 42.7k
1 vote

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

Is the friction here kinetic since the blocks are moving down. I don't know how to know when to apply kinetic friction and when to apply static fricion. When motion is given I understand and use ...
• 75.7k
1 vote

### Is the person in the picture doing any work?

During the process of accelerating, he will indeed have to apply a horizontal force. However, once he is up to speed, he can continue moving that way indefinitely without any more expenditure of ...
• 50.6k
1 vote

### Case study on inertia

Assume your feet are on the floor of the bus and your upper body is leaning against a wall in the bus. Most shoes are designed to be non-slip, so your feet won't move. Also, your feet, ankles and ...
• 1,073
1 vote

### Case study on inertia

The whole body moves forward, but friction between the person's foot and the floor helps keep the relative motion near the foot low. That being said, as a word from the wise, the human body is an ...
• 50.6k
1 vote

### Case study on inertia

Because static friction between the person’s feet and the floor tends to restrain the lower part of the body of a person standing in the bus, while the upper body will tend to move forward if not ...
• 75.7k
1 vote

### How is mechanical energy conserved in inclined plane-block system?

System block and plane. The block loses gravitational potential energy and the block and plane gain an equal amount of kinetic energy as the are no dissipative forces, eg friction. Two forces on the ...
• 98.6k
1 vote

### Why do we have an opposing force in dynamic equilibrium?

it is said that the force of the friction is equal to the pushing force wouldn’t then the vectors add up to0 and the create would be still)? Thanks a lot You can push a box on a floor at constant ...
• 75.7k
1 vote
Accepted

### Increase in tension due to weight

There is no relationship between $T_0$ and resulting tension due to weight. $T_0$ depends only on the weight of the string (0 in ideal cases). So, there is no relationship. I am sure that helps.
1 vote

### Why are my heavier objects sliding on a smaller incline than lighter objects? Coefficient of Static Friction

I think the reason is to do with indentation. If you place a heavy object of a soft surface for a while the object sinks into the surface and leaves an indentation or impression of the object when it ...
• 7,441
1 vote

### Why are my heavier objects sliding on a smaller incline than lighter objects? Coefficient of Static Friction

I have written similar things in other answers. But getting this message out depends on repeating it to some extent. A John Yeager, a well-respected rock mechanics expert, has a famous quote that ...
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