# Tag Info

Accepted

### Is it correct to say that it is theoretically impossible for perfect rigid bodies to exist?

You are right. Perfectly rigid bodies are an idealization, like point particles or massless frictionless pulleys. They do not exist. But they are useful. Plenty of objects exist that are so rigid that ...
• 25.8k
Accepted

### Do electrons have inertia?

Inertia is the resistance of any physical object to a change in its velocity. This includes changes to the object's speed, or direction of motion. An aspect of this property is the tendency of objects ...
• 221k

### Trying to understand Newton's Second Law

It is normal that an object has a constant velocity while we apply a constant force. But it is an indication that there is another force acting in the opposite direction, usually some friction force. ...

### Trying to understand Newton's Second Law

My thinking here is that change in position means change in velocity This is wrong. A change in position does not necessarily mean a change in velocity. If an object is moving at a constant velocity ...
• 7,265

### Trying to understand Newton's Second Law

$a$ is the rate of change of velocity. So if $a$ is zero, $v$ is constant and doesn't change over time. So while you're applying a force, the velocity is changing and $F=ma$. After the force stops, ...
• 407

### Does this prove that the force and momentum formulas are wrong?

Assuming that OP means Newton's second law by force formula, Note that it says $$\mathbf{F}_\text{net}=m\mathbf{a}_\text{net}$$ In you situation, you are putting two forces from opposite sizes so that ...
• 10.9k

### Is it correct to say that it is theoretically impossible for perfect rigid bodies to exist?

Not quite. You are correct that rigid bodies do not exist, but this is not the reason. Your assumptions imply that for a velocity to go from a positive value to a negative value, it must go through ...
• 42.7k

### Do electrons have inertia?

In physics, the phenomenon of inertia is in a category where an exhaustive explanation for it is not available (and may never be). The point is: in order to have a theory of physics at all the ...
• 15.2k

### What is the work done by friction on a body from the perspective of different observers using the formula $-μmgl$?

Actually, $l$ is not a constant. The different observers measure different values for $l$. The discrepancy in the change in KE is entirely explained by this disagreement on $l$. So, for a block ...
• 64.4k

• 991
1 vote

### How does a sliding object stop moving by the effect of kinetic friction, if kinetic friction is constant and Fk can't be greater than Fapp on its own

Imagine you throw a ball vertically upward against the force of gravity , the ball would move some distance vertically and then stop due to force of gravity. When you throw the ball , you exert force ...
1 vote

### How to find the force exerted by continuous jet of water on a wall?

If its solid or liquid the law doesnt change, so lets just apply Newtons second law again. $$F=\frac{dP}{dt}=\dot{m}(v_f-v_i)$$ Where $\dot{m}$ is the amount of mass hitting the wall per unit time ...
1 vote

### Trying to understand Newton's Second Law

If I apply a force on an object at rest and it’s velocity is constant (after force is applied) wouldn’t that mean that the acceleration is 0? After the force is applied, i.e. when the force is no ...
• 125
1 vote

### Trying to understand Newton's Second Law

There's two things to note here. The first one is that both quantities $\mathbf{F}$ and $\mathbf{a}$ are actually functions of time, not just numbers. If one wants to be explicit, one can write this ...
• 17.1k
1 vote

### Trying to understand Newton's Second Law

If I apply a force on an object at rest and it’s velocity is constant This is not possible. Newton's first law already says that if you apply force, velocity will change. So the situation you ...
• 11
1 vote
Accepted

1 vote

### A problem Understanding how a two-body system of planets starts rotating around barycentre

In your model, there is no expectation of circular motion. The usual theoretical understanding is that planets form from gas and dust in an accretion disk. The gas and dust in a disk moves in nearly ...
• 3,261
1 vote

### Does this prove that the force and momentum formulas are wrong?

When you say that force and momentum formulas are based on motion, that is not completely true. For example, Hooke's law says that the degree to which a spring is stretched or compressed is ...
• 18.3k

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