# Physics - Mechanics - Kinematics

Detailed revision notes on Kinematics to help with revision for Mechanics

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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

## Other pages in this set

### Page 2

Here's a taster:

Velocity is the speed of an object in a particular direction or the rate of change of displacement
Velocity has a magnitude and a direction therefore a vector quantity
The word equation for velocity is:
Velocity (m/s) = change in displacement (m) / time taken (s)
Speed is how fast an object is travelling in any direction
Speed only has a magnitude and therefore a scalar quantity
Displacement against time graphs
We can represent the changing position of a moving object by drawing a displacement…read more

### Page 3

Here's a taster:

Velocity is defined by the following word equation:
velocity (m/s) = change in displacement (m) / time taken (s)
The gradient of a displacement against time graph is equal to velocity:
v = delta s / delta t
A scalar quantity has only magnitude. A vector quantity has both magnitude and direction.
Distance and speed are scalar quantities. Displacement and velocity are vector quantities.…read more