![]() ![]() The leaning turns that energy into forward acceleration. Vertically you lose and recover potential energy as your legs work. Rather it lets your legs work both vertically and horizontally. It should be understood that leaning doesn't add a continuous source of energy. When you lean against acceleration you're using that to keep yourself balanced. It's the pull of gravity that gives you potential energy that you can turn into horizontal kinetic energy as you fall over. That's because you need gravity for leaning to mean anything. Unless you're experiencing turbulence (which is also acceleration) the stick will behave the same as it did when you were standing still.īut do this in space and the leaning is no longer a thing. Let it lean in any direction and to return it to balance it you'll have to accelerate it in the direction of the lean.ĭo that on a moving train or a flying plane and you'll find the stick behaves the same way. You can prove this to yourself by balancing a stick on your hand. So long as your speed isn't changing there is no acceleration and so no leaning. If you aren't accelerating you don't need to lean. To avoid falling over you lean into the curve. 2Īs you move through a curve you accelerate towards the center of the curve. At the end of a long enough race you'll be going as fast as you can. If you aren't accelerating you shouldn't be leaning (or you'll fall over). You see this when you wish to accelerate significantly 1 and not fall down. You don't need to pull a load behind you. The leaning forward allows the person to use gravity to counter the torque. So the torque from my legs might easily be 10 times the torque of the weight that I'm pulling. The problem is that the force on the feet is about as far as it can be, whereas if I'm grasping something with my arms at about waist level, that's about as close to my center of mass as it can be. Torque says we should multiply by the lever arm, which is to say the distance from about this person's belly button where the line of the force intersects them. The cart’s reaction force on the person is thus backwards, the force on the feet is forwards, and they are about the same magnitude. The forces are roughly comparable: the horizontal component to force on the feet always points forwards when walking forwards and has to provide also the horizontal component to force on the cart. Once you know to look here the rest of the analysis is very straightforward. The conserved quantity that matters in the torque case is called angular momentum, torque is a property of force that can transfer angular momentum, and if we notice that a human is staying constant orientation, then we can conclude that they are in a state of torque balance. All of these balances are called “dynamic equilibrium” conditions. If my sink is a bit clogged and there is a standing water level in my sink, conservation of mass of the water is going to guarantee that if the water level is not changing, then water coming in from the faucet is equally balanced by water leaving, either by evaporation or by slipping around the clog. Well, the same thing can be said of any conserved quantity, it doesn't just have to be momentum. ![]() The internal forces cancel each other out.”) (It is sometimes confused with Newton's third law Newton's third law just says here that “You don't need to consider all the forces, only the external ones. So, you already know that a rigid body which happens to have a constant momentum, this constancy requires all of the external forces to sum to zero: this is force balance. Probably the easiest way to analyze it is in terms of torque balance.
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