Science - Physics

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Forces and Movement

When an object moves, in a steady line at a steady speed, you're able to calculate its average speed.

Average speed measured in metres per sec, m/s

Distance moved measured in metres/m

Time taken measured in seconds/s

EXAMPLE - A car travels 300m in 20s = average speed is 300/20 = 15 m/s

FORMULAE - Average speed = distance moved/time taken

(/ = divide)

DISTANCE-TIME GRAPHS - shows how far something travels over a period of time.

When object is stationary, the line of graph is horizontal.

When object is moving at a steady speed in a steady line, the line on graph is straight but sloped.

Steeper the line, the faster the object is travelling.

Calculate the acceleration of an object from its change in velocity and time taken.

Velocity is not exactly the same as speed. Velocity has a direction as well as a speed. For example, 15 m/s is a speed, but 15 m/s North is a velocity (North is the direction).

+ means forward, - means backwards - EXAMPLE - +18m/s = moving 18 metres per second forwards.

EQUATION - ACCELERATION (metre per second squared) = change in velocity (metres per sec) / time taken (s)

The units for acceleration are commonly written as m/s/s or m/s2. The equation for acceleration can also be represented as: a = (v - u) divided by t.

a is acceleration in m/s/s or m/s2

v is final velocity in m/s

u is initial velocity in m/s

t is time in s

EXAMPLE - a car accelerates in 5 s from 25 m/s to 3 5m/s. Its velocity changes by 35 - 25 = 10 m/s. Therefore its acceleration is 10 ÷ 5 = 2 m/s2

Deceleration, or negative acceleration, is observed when an object slows down. The units are the same as for acceleration but the number has a negative symbol before it. For example, the car slowed down at -1 m/s2.

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Forces and Movement (continued)

The velocity of an object is its speed in a particular direction.