# Tag Info

## Hot answers tagged collision

43

The assumption that you are making here is that with the same motion of a punch, that you are applying $\text{100 N}$ of force to both a wall and to the air. However, you should think about the most fundamental equation of Newton's laws, namely, $F=ma$ The most important part of this in relation to what you are talking about is that the force applied, $F$,...

42

The notion of soft or hard object depends on the velocity of interaction. Water can be soft or hard as rock depending on how fast you fall in (or surf upon). For a shock, the main thing that matter is momentum. In space, where relative speeds can be very high, a simple bolt can cause serious damage to the ISS, and simple flakes of paint cause deep ...

33

At high speeds the structure of the material becomes far less important than it is at low speeds. At high enough speeds, the issue is not whether the tomato can retain structure during the impact (it wont), but rather the issue becomes one of sheer mass. The issue is easiest to see in the tomato's reference frame, where one treats the tomato as holding ...

24

You've caught a non-intuitive part of Newton's 3rd law. It's actually applying in the case you mention, but because the objects involved are of dissimilar hardness it's easy to perceive the impact as a violation of the law. Impacts are actually really complicated. Consider this slow motion video of a punch to the gut. We won't be able to cover all of the ...

12

As Anubhav mentioned in his comment, tomato would break into pieces before it hits the plate. However, to answer the logic of the question such event is possible. A ping pong ball can rip a huge hole on the ping pong racket if it is fast enough. https://www.youtube.com/watch?v=acRnKnsddwc Update: It would make a hole, if you make enough assumptions. As ...

11

The frequency of a sound wave cannot change as it crosses the water-air boundary. The wavelength can, and does, change but the frequency cannot because if it did there would be no way to match the two waves at the interface. This means that the higher frequency is not some quirk of the sound propagation, but that the colliding stones emit a higher frequency ...

9

Photons don't directly interact with each other, but if one photon pair produced an e+/e- then the second photon could interact with that pair. The interaction has to conserve the energy of the two photons and conserve their momentum as well of course. But yes they could (and most probably depending on their energy) just pass right "through" each other.

7

There is no doubt the Newton's third law holds in this situation. The source of confusion might the fact that you are neglecting the time interval of the collision so it is better to approach this problem by the momentum principle. The impulse of a force $F$ is given by $$I\equiv\int_{t_1}^{t_2} Fdt=\Delta p,$$ where $\Delta p$ is the momentum change due to ...

7

TL;DR: The physics of hitting things are not as easy as exerting a constant force on something. What I am trying to say with that is that Newton's law of course applies, but it would be more obvious to see it if you were just pushing/leaning against the wall with your weight. Then I'd say the two walls probably feel roughly the same. So what is different ...

6

The pulley (and the attachment to the ceiling) are part of the system here. Because of this, you cannot simply use conservation of momentum on the three given masses. If the final velocity were $v$, then the total energy of the system would have increased since both the pan and counterweight would be moving and the other mass would not have slowed. You ...

6

Assume that after each bounce the velocity decreases in a factor $\xi\in(0,1)$. This means: if the velocity before hitting the floor is $\dot y$, then the velocity after hitting it will be $\xi \dot y$. Let $y(0)=0$ be the initial height and $\dot y(0)=v_0$ be the initial velocity. We choose the units so that $g=1$ and $v_0=1/2$, where $g$ is the ...

6

What makes you think that the maximum force you applied to the dry wall was anything like the maximum force you applied to the brick? It certainly wasn't. The dry wall gave way much before you were able to attain the same force as applied to the brick. Try punching the air and see how much force you are able to apply. The experimental evidence that the ...

5

There is no such thing as classical motion of an electron in an atom. The quantum states electrons in an atom are in are atomic orbitals, which possess a definite energy, but not a definite position. The Bohr model of the electron, in which electrons are thought of as classical particles orbiting the nucleus, is false. The question whether or not two ...

5

This is the same problem as the famous question states: which is heavier, 1k of feathers or 1kg of iron? It requires many more feathers to get 1kg of them, so it confuses most people. In this case, it requires you to have a big wing to be able to apply a force of 100N on air.

5

Yes, because even just a water (a big drop of water) would do this. It has been written, in many sources (here for instance), that at high impact speeds the water (or even gas) is as hard as a concrete or glass. Mostly it is about crashing into water at high velocity, but water crashing into something would probably not make any difference.

5

Car collision "damage" usually goes with the energy in the zero momentum frame. In both cases that is (since in the zero momentum frame, the two cases are equivalent, assuming the masses of the cars are equal): $$E_1 = 2 \times \frac{1}{2} m v_{rel}^2 = m \left( 30 \frac{km}{h} \right)^2$$ Therefore a priori there is no difference between the two situations....

4

No, Newton's third law is not violated. According to Newton's Second Law, we have that force is the rate of change of momentum with time, i.e. $$F=\frac{\Delta p}{\Delta t}$$ where $p$ is momentum and $\Delta t$ is time elapsed. When Punch Strikes Wall Initial momentum of fist = $mv$ Final momentum of fist = $0$ Force applied = $\frac{mv-o}{t} = \frac{... 4 When two objects collide, they transfer momentum because they exert an equal and opposit force on each other (Newton's third law), and$\Delta p = \int F dt$. In order to know how fast an object moves after a collision, we need to know the velocities and mass of the objects before the collision and how elastic the collision is (conservation of kinetic ... 4 If you fire your projectile on a rigid target it will move, no matter what the diameter of your bullet is. All that counts in this scenario is the momentum and kinetic energy. If the target is a soft target you do also move the part of the target that is directly hit by the bullet, but since this part has a smaller area when you use a smaller caliber the ... 4 The important point here, which I think has been missed so far, is that momentum goes like velocity while energy goes like the square of velocity: $$p = mv$$ but $$E = \frac{mv^2}{2}$$ So let's consider a small object with mass$m$hitting, and sticking to, a much larger object with mass$M$, if the initial velocity of the small object (bullet or baseball) ... 4 Your gut feel is correct. Both are exactly the same. Look at the acceleration in both scenarios. 35 mph to 0 in the time it takes for the cars to fold up and stop. Everybody gets this wrong. Good question. 4 If I understand correctly, you are asking if a meteor impact could (i) slow the Earth's rotation on its axis or revolution around the Sun enough to account for the 8 to 12-fold decrease in longevity of human-kind measured in Earth days/years; and (ii) cause 40 days of torrential rain, resulting in sufficient inland flooding to float a large wooden boat. An ... 4 It can't fall slower as the first cosmical speed (7.8 km/s), which is still very high. Although it would cause much smaller destruction as it would hit directly with the mean speed of the meteors (10-70km/s). The lower angle of the hit doesn't play a significant role, because considering its mass, the interaction with the atmosphere will be probably ... 3 Liquids and gases are both fluids, meaning they flow(duh) and will take the shape of their container. Gases will expand to fill the container, while liquids will not. Solids are not fluids and do not conform to their container's shape. Yes, I know you can squeeze things to fit (e.g. a sponge), but only at the cost of distorting the structure and storing ... 3 Usually absolutely nothing. Electromagnetism is linear, which means that the result of doing something with two photons is the superposition of the results of doing something with each one individually. By that reasoning, since one photon by itself just goes on its own merry way, then two photons, even if they go near each other, just go along on their ... 3 There is a general definition of a center of mass in General Relativity, which was proposed by Dixon (W.G. Dixon, Il Nuovo Cimento 34, 317 (1964)) and whose existence and uniqueness were proved by Beiglböck (W. Beiglbock, Commun. Math. Phys. 5, 106 (1967)). These are very old papers, so that people have been working since long ago on this topic. In ... 3 None of these answers really address the question; mostly they just reiterate physics principles that I suspect the poster already understands. The question is saying, 'If kinetic energy changes in different types of collision, then the final velocities must be changing. If the final velocities are changing, the final momentum must be changing, but momentum ... 3 Suppose someone suggests that following a perfectly elastic collision, two billiard balls are each traveling twice as fast as they were before (and opposite to their original directions). You can't prove him wrong using conservation of momentum, but you can prove him wrong using conservation of energy. Therefore conservation of energy has implications that ... 3 Let's revisit "force on impact" for a moment. I will consider a "sticky" ball of mass$m$traveling at velocity$v$at a stationary wall. When it hits the wall (and sticks), what is the maximum force felt by the ball / wall? That is actually not a trivial question to answer. The ball has momentum$p=mv$, and if the impact time (time for the ball to come to ... 3 I am only going to leave a brief answer, seeing that the comments are very accurate. The paradox can simply be resolved by considering the elastic nature of all the objects. How so ever instantaneous might the$dt\$ or the time of collision seem to the human eye, actually it occurs over a small duration, based on the elasticity of both the objects involved in ...

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