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# Mechanics

11SCP Mechanics Achievement Standard
by

## Carolyn Green

on 17 May 2012

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#### Transcript of Mechanics

Mechanics
Motion
Speed
Distance
Speed-time graph
Distance-time graph
Energy
Kinetic
The energy that moving objects have.
Potential
The energy that objects have stored in them.
For example chemical potential,
Force
A force is a push, pull or twist.
Mass V Weight
Gravity
Work
Work done is equal to the force applied times the distance travelled.
If the object does not move then no work is done.
Work done is measured in Joules (J)
Power
Power is the rate of doing work, this means it is how much work is done over a period of time.
Or Power = Work done / time
Power is measured in Watts (W). One Watt is one Joule per Second
Pressure
Conservation of energy
Energy cannot be created or destroyed, only change from one form to another
Chemical potential
Gravitational Potential
Elastic Potential
Kinetic Energy
Conservation of energy in a runner
The runner eats food which has chemical potential energy
The food is turned into kinetic energy as they move
Not all the chemical potential is turned into kinetic energy, some becomes heat.
Pressure
Pressure is the amount of force per unit of area
So a larger force or smaller area will increase the pressure
The heel of these shoes is 0.001cm sq, the mass of the girl is 60kg- this means she exerts a force of 600N on the floor.
Calculate the pressure exerted...
From the distance time graph you can calculate the speed by calculating the gradient of the line.
Calculating the gradient (slope) of a line
rise is how much it has gone up, run is how much the graph has gone across.
On this graph the rise is 7 and the run is 10
the gradient of the graph is 7/10= 0.7
From a speed time graph you can calculate the acceleration using the gradient of the line as well as the distance travelled using the area under the graph.
The acceleration of the object is rise/run= 7/10= 0.7ms-2
The distance travelled in the first 10s is the area under the graph in the first 10 s.
The area of a triangle = 1/2 x base x height
area = 1/2 x 10 x 70
Drawing force diagrams
-Use a ruler
-Clear arrows of an appropriate size
-Draw from the centre of the object, pointing out
Mass v Weight
Weight is a force downwards due to gravity and is measured in Newtons (N), your weight force changes with gravity so if you went to the moon you would weigh less but on Jupiter you would weigh much more.
Weight=mass x gravity
Mass is a measure of the amount of gravity in an object, this would not change even if you were on another planet.
Newtons Laws
Newton's three laws of motion describe the relationship between forces and the motion they produce
First Law
The velocity of an object remains constant unless there is an outside force applied
Second Law
The acceleration of an object is proportional to the force applied and inversely proportional to the mass.
This means Force= Mass x Acceleration
F=ma
Third Law
The forces of two objects on each other are always equal and in opposite directions
"To every action there is an equal and opposite reaction"
Using Newtons Second Law:
Eg A tennis ball with a mass of 50g, accelerates at 2m/s2. Calculate the force applied to the ball.

Write what you know:
F=?
m=50g =0.05kg (this must always be in kg)
a= 2m/s2 (this must always be in m/s2)

Write the formula:
F=ma

Substitute:
F= 0.05 x 2

Calculate:
F=0.1 N
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