# Gravitational Field LO (a)

Think about it: How can two objects exert attractive force on each other when they are not in contact with each other?

Every object sets up a gravitational field around itself due to its mass.  When two objects enter each other’s gravitational fields, they will be attracted towards each other.  Hence, a gravitational field (an example of force field) is a region of space in which any object lies in it experiences a gravitational force towards the object that creates the field, due to its mass.  (For your information, magnetic fields and electric fields are also examples of force fields.)

## Inquiry:

Gravitational field is invisible and is represented by imaginary field lines. How would the Earth’s gravitational field (both near and over large distances from Earth) looks like?

### 1)    Draw a few small (shown as blue dots) masses (using pencil) placed very near the Earth’s surface below and draw the direction of gravitational forces acting on them by Earth.

•    The gravitational field near Earth’s surface is uniform
•    The field lines should be drawn parallel to each other and of equal spacing.

### 2)     Draw a few small masses (shown as blue dots) (using pencil) placed further from the Earth surface below and draw the direction of gravitational forces acting on them by Earth.

•    The gravitational field around Earth is non-uniform.
•    The field lines should be drawn radially pointing towards the centre of Earth.

### 4)     Finally, draw a few small masses (shown as blue dots) (using pencil) placed very far in outer space from the Earth below and draw the direction of gravitational forces acting on them by Earth.

•    The gravitational field around Earth is non-uniform.
•    The field lines (use the red test mass to draw field lines) should be drawn radially pointing towards the centre of Earth.

### What can you infer from the spacing of these gravitational field lines? LO (e)

1. The closer the field lines, the stronger the gravitational field.
2. Near Earth’s surface, the field strength is approximately constant (around 9.81 m s-2) and hence the gravitational field lines are almost equidistant from each other.
3. Over large distances from Earth, the gravitational field strength decreases as it gets further from Earth and hence the gravitational field lines space out further from each other.

# Model:

https://dl.dropboxusercontent.com/u/44365627/lookangEJSworkspace/export/ejss_model_gravity03/gravity03_Simulation.xhtml