http://www.ck12.org Chapter 4. Motion and Forces
4.16 Einstein’s Concept of Gravity
- Identify limitations of Newton’s law of gravity.
- Describe Einstein’s theory of gravity and how it differs from Newton’s law.
Why is jumping on a trampoline so much fun? Its springy surface helps you jump higher than you ever could on the
hard ground. But even on a trampoline, you can’t keep jumping higher and higher. Gravity always pulls you back
down. You’ve probably known about gravity since you were in elementary school. It’s the force that pulls all objects
on Earth down toward the ground. Is that all there is to gravity? Absolutely not!
It Started with Newton
In the late 1600s, Isaac Newton introduced his law of gravity, which identifiesgravityas a force of attraction between
all objects with mass in the universe. The law also states that the strength of gravity between two objects depends on
their mass and distance apart. Newton’s law of gravity was accepted for more than two centuries. It can predict the
motion of most objects and was even used by NASA to land astronauts on the moon. It’s still used for most practical
purposes. However, Newton’s law doesn’t explainwhygravity occurs. It only describes how gravity seems to affect
objects. There are also some cases in which Newton’s law doesn’t even describe what happens.
Q: Newton expressed his ideas about gravity as a law. A law in science is a description of what always occurs in
nature. For example, according to Newton’s law, objects on Earth always fall down, not up. What is needed to
explain gravity?
A: A theory is needed to explain gravity. In science, a theory is a broad explanation that is supported by a great deal
of evidence.