eli5 How can humans push cars and pull massive things with weeks but can’t lift more than a few hundred pounds?



*weels not weeks

In: Physics


These massive things don’t have the brakes on when humans are pulling/pushing them. They have wheels and they’re designed to roll along the ground nicely once they’re already moving. When you’re going horizontally rather than vertically, gravity has much less of an effect. Gravity does slow it down through friction, aka rolling resistance, but if a car is moving on a flat road you might be surprised how far it will go on its own. So it’s just up to the humans to get them moving. Once that’s started they are moving and you can just keep that going.

Have you ever used Neutral gear in your car before? (Do NOT do this on public roads, it’s dangerous and illegal)

These machines are designed this way of course. Too much rolling resistance means more fuel burned just moving in a straight line, and that friction means something is wearing out.

The force you are fighting against when pushing/pulling is friction. This isn’t as much force as the direct downward force of gravity when you try to lift something.

Additionally, you can use your weight to push and pull (e.g., leaning into the direction you’re pushing). When lifting, you are relying entirely on your muscle capacity. And lastly, lifting an object really depends also on its geometry. Awkwardly sized objects are hard to lift. When pushing, it’s not as big a deal because you are not personally trying to stabilize the object (which means actively fighting the force from torque). Ideally, an object is already stable on the ground.

Because to lift something up, you need to overcome 100% the force of gravity upwards before it even begins to move. To push or pull a thing on wheels you just need to apply any amount of force greater than the friction of the bearings that the wheels are attached to and it will start moving.

This video explains it in depth, it focuses on the fact that the tesla cyber truck was able to pull an f150, it’s not exactly what you’re asking but it gave me a good understanding of the physics behind pushing/pulling things