GCSE Additional Science: Physics

FORCES & MOTION

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  • Created by: Bennifer
  • Created on: 27-01-10 19:50

Forces & Acceleration

Resultant Force = overall unbalanced force

Any resultant force produces acceleration

Force (N) = Mass (kg) x Acceleration (m/s2)

F=ma

Force is measured in Newtons (N)

Example 1

A car travels at a steady speed… the thrust force is equal to the drag force.

This does not necessarily mean that the car is stationary, but it does mean that the car is neither accelerating nor decelerating.

Example 2

A car accelerates from rest.

The forward thrust is larger than the backward drag.

The car will accelerate in the direction of the greater force, in this case the forward thrust

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Velocity & Acceleration

Speed =

How fast something travels

Speed (metres per second, m/s) = distance travelled (metres, m) time taken (seconds, s)

Velocity

How fast something travels in a direction

Acceleration

Change in speed in a given time

Acceleration (metres per second squared, m/s2) = change in velocity (metres per second) time taken (seconds, s)

Distance vs. Time Graph

distance v time (http://www.revisionworld.co.uk/files/d_t%20copy.jpg)

Speed vs. Time Graph

speed v time (http://www.revisionworld.co.uk/files/s_t%20copy.jpg)

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Newtons First Law

Balanced forces = constant velocity

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Newtons Second Law

F=ma

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Newtons Third Law

"every action has an equal and opposite reaction"

e.g. a book on a table

The book’s weight (mass x gravity) pushes down on the table

The table pushes back with a reaction force

Size of action (weight) = size of reaction

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Summary

distance (m) = speed (m/s) x time (s)

Velocity is speed with a direction e.g. 10m/s Northwards

Acceleration (m/s2) = change in speed (m/s) / time taken (s)

Acceleration = (final velocity - initial velocity) / time taken (s) or a = v-u/t

Balanced forces = constant velocity (this can be stationary)

Unbalanced forces (resultant) = change in velocity (+ve / –ve)

Every action force has an equal and opposite reaction force

Force (N) = mass (kg) x acceleration (m/s2)

The difference between opposite forces = resultant force. An object will accelerate / decelerate according to its size

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