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3
votes
1answer
40 views

What forces the maximum speed of a cyclist on a steep climb?

I know that on a flat road drag is the main force, I have to provide as much force as the drag (and the friction in the drive train) produces. I can also see that the faster I ride, the harder it gets ...
1
vote
2answers
46 views

Force, work and the apparent disappearance of Mechanical Energy [duplicate]

A man exerts force on a wall of bricks. The man must have consumed the energy he possessed (mechanical energy?) to exert the force. The man sweats and tires himself out but the wall does not move. ...
-1
votes
1answer
43 views

Same amount of calories burned for half the reps and double the weight? [duplicate]

So I was looking at the work= force x distance equation and was just wondering if for example I normally do 100 dead lifts at 100 pounds. Would I get the same calories burned if I did 50 dead lifts ...
0
votes
0answers
28 views

When we push a wall, we get tired Why? [duplicate]

When we push a wall the wall does not move so, no work is done but still we get tired Why? What energy changes occur in this process.
0
votes
2answers
1k views

Why is unit of pressure (psi) used to determine things like bite force of an animal?

Whether in tv documentaries or journals, whenever they talk about an animal's bite force, it's measured in PSI anytime imperial units are used (ex: National Geographic, NIH Journal). Many even seem to ...
-2
votes
1answer
667 views

Why is the work done by someone pushing a cart not zero? [duplicate]

We know that when force is perpendicular to displacement, then the work done by it is zero. If this is true, then why do the vegetable vendor (who pushes the cart by applying perpendicular force) ...
0
votes
4answers
7k views

What force enables us to walk?

When we walk, we apply a force $F$ on the earth at an angle $\theta$ . Thus, by Newton's third law, $$ F_{\text{me, earth}}=-F_{\text{earth,me}}$$ Therefore, the earth exerts a reaction force on us, ...
0
votes
1answer
94 views

Determining units in a cone and plate flow system

I am building a cone and plate system as depicted in Figure B below. My goal is to solve for the appropriate rotational speed, ω, given the following parameters: τ - 15 dynes/cm^2 μ - 0.9 centipoise ...
2
votes
1answer
54 views

What amount of force could be created by a person “swimming” in air?

Had a question on a physics test, a person is at rest on a frictionless surface and can not throw anything, can they move? I said yes, by "swimming" against the air and got docked because "it wouldn'...
20
votes
4answers
20k views

Why do whips hurt so much?

What exactly is the mechanism that makes a whip deliver such a strong impact? Elasticity, torque, or pressure? Just hitting something with a plank doesn't deal nearly as much damage. What's the ...
4
votes
1answer
246 views

Relation between Casimir and hydrophobic effects

Background Some years ago I was studying "Fundamentos de biología" (Biology fundamentals) and learned how the lipids create a bilayer due to the water repulsion. Some time later I learned that this ...
8
votes
2answers
10k views

How can an an ant lift 50 times its own weight and pull 30 times its weight?

According to many sites like this one, an ant can apparently lift 50 times its own weight and pull 30 times its weight. Is it true? Can it be proved using physics? Though most sites agree that an ...