When a person bumps into something or has something dropped on them and a bruise forms, does it form because of the object hitting the person or from the person exerting a force on the object to keep that object from pass through their skin?

Answer The bruise forms because of the force exerted on the person by the object. When an object hits you, it's obvious that the object pushes on you. But the object also pushes on you when you hit it. In... Read More »

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If space is curved and gravity is not really a force (as per Einstein), how is it that an object can slingshot around a planet and gain kinetic energy Where is the extra energy coming from Which object converts mass to energy; the object or the plane?

When a small object such as a satellite arcs around the back side of forward moving planet, the satellite's speed and energy increase while the planet's speed and energy decrease. The planet has gi... Read More »

If you lifted an object with a hanging scale on earth and it read 15 N, would it read the same on Jupiter What about the gravitational force pulling the object down Wouldn't that alter the reading on the scale Would you have to calibrate another scal?

No, the scale would not read the same on Jupiter, and there would be nothing wrong with the scale! On Jupiter, the object would simply weigh more than on earth. Its mass wouldn't have changed and i... Read More »

In high school, we said that an object on the ground has zero gravitational energy, while an object above the ground has some. But if a hole opened up in the floor, the object on the ground would fall - so it must have SOME potential energy, right At?

You've brought up an interesting subject. Many quantities in physics are only well defined relative to some reference point. For example, your velocity is only defined relative to some reference fr... Read More »

When you spin an object around a fixed point, a sling for example, does the object at the end build up energy that causes it to shoot out quickly when released?

Yes. As you whip the object around on a string, you are doing work on it. You do this by making subtle movements with your hand, exerting forces that aren't exactly toward the center of the circle.... Read More »