For the reason that change in kinetic vitality remains to be zero, which means the constructive change in gravitational potential vitality is the same as the unfavorable of the change in inner vitality. As an example you will have a mass of 75 kilograms (165 kilos). Which means transferring up 1 meter would scale back your inner vitality by 735 joules. That is referred to as understanding.

Climbing Stairs vs. a Stair Climber

Now we are able to return to the unique query: What does the work-energy precept say about stairs versus a stair-climbing machine? Nicely, we already did the physics of stair climbing. It is the identical calculation if you happen to get on high of a 1 meter desk or climb 100 tales—it is only a totally different worth for the peak. However suppose you keep in the identical place whereas the steps transfer beneath you. If somebody is measuring your ahead movement, they’d say your velocity is zero. Your peak additionally does not change, so now the work-energy equation seems like this:

This says the change in inner vitality can also be zero, which implies you do not burn any energy. I imply, that may’t be proper … proper? Then how will we repair this? I’ll use a pleasant instance based mostly on this video from Steve Mould. It goes like this: Think about you might be climbing up a downward-moving escalator. Once more, an observer on the bottom would see you as stationary. Nonetheless, we may additionally measure your velocity from the reference body of the escalator, and you’ll be transferring up.

In reality, if the escalator had partitions and a ceiling, you would not have the ability inform that you simply had been staying in place. You would not even know the steps are transferring. For the reason that stairs are transferring at a relentless velocity (zero acceleration), this could be an inertial reference body. In physics, any inertial reference body is as legitimate as another reference body—the fundamental legal guidelines of physics stay the identical. So, from the attitude of the escalator body you are transferring up and doing work. It is the identical as if you happen to had been strolling up a stationary body.

However Truly, the Stair Climber Is More durable

I mentioned that the stair climber and climbing stairs had been the identical—however they don’t seem to be. In reality, climbing up 100 tales is simpler than the equal distance on a stair climber. Does that appear loopy? It’s a little loopy. The rationale they’re totally different is as a result of the gravitational subject (g) isn’t actually fixed.

Keep in mind, we outlined the gravitational potential vitality as U = m x g x y? That is not likely incorrect, however it’s a little deceptive. Truly, the gravitational potential vitality for the Earth-person system can be outlined as the next: