# OCR Physics mechanics

- Created by: HenryCawley
- Created on: 05-01-14 18:36

**Yo, here are revision notes for the entire OCR Physics mechanics, made using the 2014 specifications, so should be useful. Thanks**

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**Module 1 Motion**

**Physical quantities and units**

some physical quantities consist of a numerical magnitude and a unit.

Mass = kilogram kg

Length = meter m

Time = second s

Temperature = kelvin K

electric current = ampere A

pico (p) = 10^-12

nano (n) = 10^-9

micro ( = 10^-6

milli (m) = 10^-3

centi (c) = 10^-2

kilo (k) = 10^3

mega (M) = 10^6

giga (G) = 10^9

tera (T) = 10^12

mass of a person - 70kg

height of a person - 1.5m

walking speed - 1ms^-1

speed of a car on a motorway - 30ms^-1

volume of a can - 300cm^3

density of water - 1000kgm^-3

weight of an apple - 1N

e.m.f. of a car battery - 12V

current in a domestic appliance - 13A

**Scalars and vectors**

Scalar - only have magnitude - speed, mass

Vector - have magnitude and direction - acceleration, displacement, weight

use pyphagoras and trigonometry to determine resultant force

**Kinematics**

**displacement** - a vector quantity that refers to the change in meters of the overal position from the origin.

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**instantaneous speed** - a scalar of the rate of movement of a body expressed as the rate of change of position with respect to time at a particular point.

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**average speed** - the distance travelled divided by the time

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**velocity** - is a vector quantity that refers to the rate at which an object changes its position.

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**acceleration** - the rate of change of velocity

average speed = distance/time

acceleration = change in velocity/time

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**velocity** - the gradient of a displacement-time graph

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**displacement** - area under a velocity-time graph

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**acceleration** - gradient of a velocity-time graph

Linear motion

V = U+at for free fall g = a = 9.81ms^-1

S = ((u+V)/2) x t

S = ut + 0.5 x at^2

v^2 = u^2 + 2as

Aristotle believed that heavier objects fall faster than lighter ones, however Galileo disproved this with the inclined plane experiement. He timed using a water clock balls rolling down a slope in a groove, finding that the distance travelled was proportional to the time squared. Proving acceleration is constant.

Experiment to measure the acceleration of free fall

1) measure h

2) flick the switch simultaneously starting the timer and releasing the ball

3) The ball falls through the trapdoor stopping the time

h = 0.5 gt^2

Error

measurement of h

switch delay

air resistance

**Module 2 forces in action**

**Force**

**net force** = mass x acceleration (F = ma)

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**newton** - a force required to give a mass of 1 kg of 1ms^-1

apply uvast and F=ma to analyse the motion of objects.

The special theory of relativity states that the mass of an object increass as it apporaches the speed of light, so that we can no longer use the equation F = ma.

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