# gravity

## gravity and weight

Weight measures the force of gravity pulling downward on an object. The SI unit for weight, like other forces, is the Newton (N). On Earth, a mass of 1 kilogram has a weight of about 10 Newtons because of the pull of Earths gravity. On the moon, which has less gravity, the same mass would weigh less. Weight is measured with a scale, like the spring scale shown in the Figure 1.1. The scale measures the force with which gravity pulls an object downward. To delve a little deeper into weight and gravity, watch this video: Click image to the left or use the URL below. URL:

## practice

At the following URL, read about gravity and tides. Watch the animation and look closely at the diagrams. Then answer the questions below. 1. 2. 3. 4. 5. What causes tides? Which has a greater influence on tides, the moon or the sun? Why? Why is there a tidal bulge of water on the opposite side of Earth from the moon? When are tides highest? What causes these tides to be highest? When are tides lowest? What causes these tides to be lowest?

## defining gravity

Gravity has traditionally been defined as a force of attraction between things that have mass. According to this conception of gravity, anything that has mass, no matter how small, exerts gravity on other matter. Gravity can act between objects that are not even touching. In fact, gravity can act over very long distances. However, the farther two objects are from each other, the weaker is the force of gravity between them. Less massive objects also have less gravity than more massive objects.

## earths gravity

You are already very familiar with Earths gravity. It constantly pulls you toward the center of the planet. It prevents you and everything else on Earth from being flung out into space as the planet spins on its axis. It also pulls objects that are above the surfacefrom meteors to skydiversdown to the ground. Gravity between Earth and the moon and between Earth and artificial satellites keeps all these objects circling around Earth. Gravity also keeps Earth and the other planets moving around the much more massive sun. Q: There is a force of gravity between Earth and you and also between you and all the objects around you. When you drop a paper clip, why doesnt it fall toward you instead of toward Earth? A: Earth is so much more massive than you that its gravitational pull on the paper clip is immensely greater.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

gravity acts only between objects that are touching.

``````a. true

-->  b. false
``````

the strength of gravity between two objects depends on their

``````a) size.

b) volume.

-->  c) mass.

d) all of the above
``````

which of the following objects has the greatest gravity?

``````a) the moon

-->  b) the sun

c) earth

d) you
``````

there is gravitational attraction between you and every object around you.

``````-->  a. true

b. false
``````

weight is measured with a balance.

``````a. true

-->  b. false
``````

## diagram questions

No diagram questions associated with this lesson