Hot answers tagged forces
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The horizontal component of running is believed to be fairly negligible for humans. Some research suggests that the limit isn't strength related at all, but design --- in particular, based solely on power, humans could theoretically run up to almost 40 mph. The issue is two fold: first, our limbs are actually too heavy, for big strength (e.g. climbing in ...
6
Suppose that you exert the force with angle $\theta$ (with respect to ground). Then you will have:
$$\mu(mg-F\sin(\theta))=F\cos(\theta)\text{, so }F=\frac{{\mu}mg}{\cos(\theta)+{\mu}\sin(\theta)}.$$
Now, if you minimize this function with respect to $\theta$ you will find that
$$\tan(\theta)=\mu.$$
Replacing this $\theta$ (a function of $\mu$) for ...
6
Non-relativistic mechanics can't. Massless objects travel at the speed of light. The only reason to introduce a massless string is so that you can get some effect from the string without having to worry about the string in calculations. As soon as you start worrying about forces on the string causing it to accelerate you've violated the whole reason for ...
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The car's engine tries to make the wheels turn. However, the wheels encounter friction against the road so they cannot just spin. As the road has much higher inertia than the car, it will not move when the wheels want to turn. Instead, it is the car that moves.
The end effect is that the engine pushes against the road, just as you do when you push the car: ...
5
Gravity is viewed as a force because it is a force.
A force $F$ is something that makes objects of mass $m$ accelerate according to $F=ma$. The Moon or the ISS orbiting the Earth or a falling apple are accelerated by a particular force that is linked to the existence of the Earth and we have reserved the technical term "gravity" for it for 3+ centuries.
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$F=ma$. If $F=0$, and $m=0$, $a$ can be anything. Most physical laws are not "A causes B". They usually say that "A and B can coexist in these conditions". So, it is not necessarily "Force causes acceleration". It is "an accelerating body can coexist with a force if $F=ma$"
The net force on a massless string is always 0 -- it has to be (otherwise it will ...
3
A constant net force means:
$$\Sigma\vec{F}=\frac{d\vec{p}}{dt}=C$$
where $C$ is some constant. This means that
$$\int \ dp=p=C\int\ dt=Ct+p_0$$
where $p_0$ is the initial momentum. Now, you can easily verify that
$$p_2-p_1=\Delta p=Ct_2+p_0-Ct_1-p_0=C(t_2-t_1)=C\Delta t$$
In particular, you see that $\Delta p \neq \frac{dp}{dt}$, unless $\Sigma ...
2
Gravity is still viewed as force for better understanding because not all have Einstein's IQ to see curvature of more than 2 dimensions.
Gravity is a force, but not a REAL force. Try pushing rat and elephant over a frictionless surface so that both feel same acceleration. Common sense says that you need more force for elephant.
It means that gravity is a ...
2
Perhaps some insight into this problem can be gleaned from relativity. In relativity, the EM field is represented by a two-form (i.e. with 6 components). When this two-form is fed a current to act upon, this yields a force--or rather, four-force, so you get power as well as force.
What does this mean? Well, you can feed the four-force any timelike unit ...
2
The slingshot effect is in fact only a transfer of angular momentum from one body to another. So for example if you're using Jupiter for a swing by manoeuvre with your satellite, you do nothing more than slow down Jupiter (in the Sun-Jupiter-(satellite) system) and speed up your satellite. Of course because of the huge difference in mass, you only see a ...
1
You haven't given us enough information to solve the problem. Is there any motion? Do you know the weight of the board? Anything else?
Typically, lever problems have two types of equations that can be useful. The first is just the standard $\sum_i F_i = m\, a$. Note that this is the sum of all the forces. For example, in your picture, the sum of all ...
1
For pushing it up, we have to overcome friction(act downwards) as well as the $mg\sin\theta$. So, $$3N=f+mg\sin\theta$$
Now the block is just slipping , so friction is acting upwards, and so does the force applied externally.So,
$$N+f=mg\sin\theta$$
Eliminate $N$ and use $f=\mu mg\cos\theta$.
Solve for $\mu$ you get your answer.
1
The ground will provide all of the static friction. Imagine what would happen if the upper block contributed even a tiny amount to the static friction: It would have to move forward due to the reaction force. Having M2 inch along you pull M1 (which stays stationary) would be very strange indeed.
Static friction always acts to prevent relative motion. It ...
1
So at atomic level for same charges that repel eachother(electrons etc.), if thought of as a slingshot effect, elastic repulsive collision and buoyancy fields etc. makes repulsion a pseudo or dummy. as for like gravity is doing it all, then it will be more insightful or not?
Not.
To describe all the available data the theory has to be much more ...
1
Newton's third law doesn't imply that things can't move but it does imply conservation of momentum and energy.
Imagine a scenario where an astronaut is in orbit so they don't feel the affects of gravity. If there is an object floating and they push on it (apply a force to it) we know intuitively that the object will start to accelerate in the direction of ...
1
The total force down is 900N. Thus, the total force up must be 900N. For the rope to be in equilibrium, the force up on each side of the pulley is 450N.
Your force down is 600N, the elevator's force down is 300N. If we carry through the math, that means your net force is 150N down and the elevator's net force is 150N up.
Assuming the weigh scale is ...
1
Great question!
I would say that "force is a one-form" is a statement that has some truth to it, but it's somewhat context-dependent.
In any context where you have a metric, you can freely convert back and forth between vectors and one-forms, and the distinction between them becomes uninteresting. Examples of such contexts include relativistic spacetime ...
1
Gravity is not special at all. It seemed to be special at dawn of the 20th century but now the picture is different.
Fields are more than just forces. Fields can have their intrinsic dynamics, solitons, topological features, nontrivial vacuum.
As of force aspect, electromagnetic field makes a 4-force $qF^{\mu\nu}u_{\nu}$, and gravitational field makes a ...
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At the risk of being chided by physicist for vast oversimplification, can I provide an intuitive answer?
In a rotating frame of reference, centrifugal force exists (as does Coriolis force). Observers in rotating frames see freely moving objects travelling curved paths. They conclude that a force exists, and can even generate a formula for it. An observer ...
1
Most of the resonances detected in particle physics scattering experiments are bound states of the strong force, bound for a time interval before decay .
These are created in the interaction and seen in invariant mass combinations of the interaction products, statistically.
The distinction with electromagnetic or weak decays comes from the widths of the ...
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