# Reflection

##### 3 minutes • 551 words

## Table of contents

How can we determine this refraction quantitatively?

To answer this, we must first explain reflection.

Suppose a ball is struck from `A`

towards `B`

. At `B`

it meets the surface of the ground `CBE`

, which prevents it from going further and causes it to be deflected.

- The ground is perfectly flat and hard.
- The ball always travels at a constant speed, both when it descends and rebounds upwards.

Where will it go?

### The Directional Force

**The force that causes the speed of the ball is different from the force that causes the direction of the ball.** That direction is determined by the position of the racket.

This directional force shows that this ball can be diverted by the encounter with the earth `CBE`

.

Thus, `CBE`

can change the direction that it had towards `B`

without changing the force that gave its speed, since these are 2 different things.

This is why it does not have to stop at `B`

before bouncing off to `F`

as many of our Philosophers think. If it was stopped at `B`

then there is nothing at `B`

which can cause it to start again.

The determination to move towards a certain side, as well as movement and generally any other kind of quantity, can be divided between all the parts that compose it.

A ball that moves from `A`

to `D`

is composed of 2 others:

- A force which makes it fall from the line
`AB`

to the line`CD`

- A force which makes it go from the left
`AC`

to the right`BD`

These together lead it to `D`

along the straight line `AD`

.

The encounter with the earth can only prevent **one** of these two determinations, and not the other.

- It prevents the one that made the ball fall from
`AB`

to`CD`

because it occupies all the space that is below`CD`

.

Let us draw a circle with center `B`

, which passes through line `A`

which is the path of the ball.

The ball would have travelled from in the same time from `B`

to some point on the circle’s circumference, as it travelled from `A`

to `B`

.

This is because we suppose that:

- all the points in the circle are as distant from
`B`

as`A`

is. - the ball’s speed is always equally fast.*

## Superphysics Note

To know where on this circle the ball must end up, let us draw 3 straight lines `AC`

, `HB`

, `FE`

perpendicular to `CE`

.

- The distance between
`AC`

and`HB`

is the same as that between`HB`

and`FE`

.

Assume that it will take the ball travelling rightwards the same time to go from point `A`

to point `B`

and from `B`

to any point in the circle that touches line `FE`

. In this case, it is `F`

or `D`

.

Thus, if the Earth prevents it from passing towards `D`

, then it must go towards `F`

.

This is how reflection occurs at an angle always equal to what is called *the angle of incidence*.

For example, if a ray coming from point `A`

falls on point `B`

on the flat mirror `CBE`

, it reflects towards `F`

in such a way that the angle of reflection `FBE`

is neither greater nor smaller than the angle of incidence `ABC`

.