Could anybody explain to me why running up a hill is harder than running on level ground? I imagine it has something to do with overcoming gravity's pull? But gravity is present everywhere, yes? Is the steepness a factor?
You're increasing your potential energy, thus doing more work. In principle on a flat frictionless surface going round the Earth you would basically be able to keep moving forever once you started, moving uphill this is not so.
The force of gravity pulls you directly toward the center of mass of the Earth.
The normal force, the force that keeps you from going through solid objects like the ground, is always perpendicular to the surface.
So on a hill, the normal force is at an angle while the force of gravity is still straight downward, so less of the force of gravity gets counterbalanced by the normal force.
You're using the back of your upper legs not your ass
Less developed muscle
>So there's the force of gravity and also a normal force?
>Is this normal force your weight?
No. But on a flat horizontal surface where the force of gravity pulls downward, the normal force will push you upward with an equal magnitude to your weight, but in the opposite direction. It's what keeps you from falling right through the ground.
However on an incline, the normal force is still perpendicular to the surface, so it doesn't counteract all of the force of gravity (your weight) anymore, which still pulls you downward with a force of 9.81m/s * your mass in kg.
>Does this "normal force" have any other name?
I'm sure it does. Check google or wikipedia.
>How about if you run up and run down (0 gain in potential energy)
If you had an ideal nonfrictional environment, you would lose no energy in that case and your velocity would remain the same before you began going up the slope as when you'd finished going down it.
the normal force is the force exerted to you from the ground.
every action has an equal an opposite reaction
so your weight is pushing down on the ground, and the ground is pushing you back up
think of it in terms of kinetic energy.
if something is at a higher altitude, it has more potential energy.
it takes energy to get it up there to begin with. climing that hill is that energy.
gravitational force on a hill can be unbound into 2 forces
1. Fn = Fg * cos(alpha)
2. Fa = Fg * sin(alpha)
Fn is the normal force
Fa is the gliding force which will be trying to pull you down the hill
the greater the angle, the greater the sinus and thus the greater the gliding force
I have found a way to explain this so that even halfwits as you may understand:
Imagine you are connected to the center of the earth with a rubber band.
If you walk on even ground the lenght of the rubber band doesn't change and its not that hard for you to walk. But if you walk up a hill you pull the rubber band longer and this is so hard.
Another big factor is the aerodynamic drag. On higher ground the air pressure is smaller and the drag is thus higher.
>Another big factor is the aerodynamic drag. On higher ground the air pressure is smaller and the drag is thus higher.