Newtons 3rd law says that an object exerts the same force back. Then why is it that if I push hard enough then the object will move? Is there a name for the total amount of force an object can put against me?
In: Physics
Think of a Newton’s cradle with two spheres, one larger and one smaller.
You pick up the smaller of the two and drop it (acceleration due to gravity). It will swing into the larger sphere and the larger sphere will move away from the now-stopped smaller sphere. The larger mass will make that distance moved quite a bit smaller than the original smaller sphere. When the larger sphere swings back to the smaller one, it imparts all of its momentum and the smaller sphere moves again, measurably farther than the large one.
F=ma. This means that the original force you applied by lifting and dropping the small sphere is constant. The mass of the small sphere is constant. The mass of the larger sphere is constant. The only thing left that is changing is the acceleration. The force applied to the small sphere moves the smaller mass further.
Another example. Throw a baseball. Your mass is large, the baseball’s mass is small. You are able to throw it very far because your muscles and tendons and torque and mass all combine to allow a certain amount of force and we know through experience that is more than enough force to launch it nicely.
Now go put a car in park on a flat surface, run up behind it as fast as you can and slam your shoulder into it (don’t do this for real). You have a small mass compared to the car, so the momentum imparted to the car is not going to be enough to do more than maybe rock it a bit.
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