# Physics - Mechanics - Kinematics

Detailed revision notes on Kinematics to help with revision for Mechanics

- Created by: George Beresford
- Created on: 13-03-12 11:05

First 383 words of the document:

Chapter 1: Kinematics describing motion

What is speed and how can you determine it?

Average speed is distance moved divided by time taken or v(ms^-1) = x (m) / t(s)

If the speed is constantly changing during the time the equation will work out average speed

Instantaneous speed is the speed of an object at a given time

Alternative units for speed are: cm/s, km/s, km/h or mph

You can find the speed of something moving by measuring the time it takes to travel between two

fixed points

However this does not tell us if the car is increasing, decreasing or remaining at constant speed

Using two light gates (method 1)

The leading edge breaks the light beam triggering a timer

The leading edge breaks the second light beam stopping the timer

Speed is calculated using the equation

Using one light gate (method 2)

The leading edge breaks the light beam triggering a timer

The trailing edge breaks the same light beam stopping the timer

Speed is calculated using the equation

Using a ticker timer (method 3)

The ticker timer creates a dotted pattern describing the objects movement

Measuring the distance of every 5th dot will give the distance travelled

The time will be the same on each interval so we can draw a d/t graph

Using a motion sensor (method 4)

The motion sensor transmits regular pulses of ultrasound

It detects the reflected waves and determines the time they took to return

The computer can determine the distance and a d/t graph can be drawn

Things to consider when choosing a method

Does it give an average speed or an instantaneous speed?

How precisely does the method measure time

How simple and convenient is the method to set up?

Distance and displacement, scalar and vector

Displacement is the distance moved by an object in a particular direction

Displacement has a magnitude and a direction therefore a vector quantity

Distance is the distance moved by an object in any direction

Distance only has a magnitude and therefore a scalar quantity

Speed and velocity, scalar and vector

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