23
votes
3answers
2k views

The physical definition of work seems paradoxical

So this is possibly a misunderstanding of the meaning of work, but all the Physics texts, sites, and wiki that I've read don't clear this up for me: In the simplest case with the simplest statement, ...
0
votes
0answers
19 views

How is work done by a system in static equilibrium? [duplicate]

For a little colour: this came from my wondering why fork-lifts are hydraulically driven, rather than electromechanically. My question is this: why is it that some systems, while in static ...
2
votes
1answer
48 views

Walking & Swinging

How can I show that the most convenient way to move the arms while walking is swinging them back and forth, alternatively? To pose the question in another way: can I prove, starting from the ...
1
vote
3answers
152 views

How do birds generate thrust?

I have been watching this video carefully and I want to know how the wings of birds generate thrust. This is because the wings are more or less flapping up and down --- generating the lift. But I do ...
1
vote
1answer
124 views

Measuring energy when no work is done — comparing push-ups to planks

tl;dr Is there any meaningful (physical) way to compare the energy expended in the exercise of doing $x$ pushups in $t_1$ seconds, vs the exercise of doing the plank for $t_2$ seconds? I'm ...
-2
votes
2answers
152 views

Is two cars colliding at 25 mph the same as one car colliding into a wall at 50 mph in reference to injuries?

This question has been asked using 50 & 100 mph reference, see this Phys.SE post and links therein. However, I am interested in the potential injuries to occupants of the autos. As the one going ...
1
vote
1answer
929 views

How does the height of a jump change if the body is scaled down?

This is a physics question that appeared in the movie 'The Internship.' If you are reduced to the size of a coin and put into a blender what would you do? Apparently the answer was that with a ...
4
votes
2answers
748 views

Is any work done when I walk?

I am trying to figure out the amount of work done when I walk X miles or for X minutes. So I got Work=Force x Distance and Force=Mass x Acceleration and Acceleration=(change in velocity)/time. I am ...
1
vote
1answer
701 views

What is physics of a normal jump?

What is the physics behind a normal human jump ? when a normal human wants to jump. First, some energy is stored in their thighs and The elastic tendons Just like a spring. In mechanics and ...
4
votes
2answers
313 views

Why don't massive water-borne animals crush under their own weight when they're in water?

If you take a giant whale out of the water and put it on land for long enough, it will crush itself under its own weight. Why doesn't the animal get crushed under its own weight when it's in water?
1
vote
2answers
895 views

How does length of the bar affect force on the muscles?

Fitness Model, Rob Riches, claims that doing bicep curls with Olympic bars is different than lifting with normal bars. Biceps have always been a favorite muscle group of mine to train, but ...