# Mechanics AS Physics.

These are the key points for the mechanics unit of AS physics

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Mechanics.
Scalars and vectors.
1. A scalar has only magnitude. Examples include mass, temperature, time, length, speed
and energy.
2. Vector quantities have both magnitude and direction. Examples include displacement,
force, velocity, acceleration and momentum.
To add vectors, calculate resultant forces or calculate resultant velocities you use Pythagoras
theorem and trigonometry.
It is useful to resolve vectors, resultant forces, into horizontal and vertical components.
Motion with constant acceleration:
There are 4 constant acceleration equations. Learn them.
Acceleration is equal to change in speed divided by time.
Speed equals distance over time.
Free fall and projectile motion.
Aristotle thought that if two objects of different mass where dropped from the same height
then the heavier one would hit the ground first.
Galileo thought that all objects should accelerate towards the ground at the same rate
therefore objects of different weights should hit the ground at the same time and the reason
this was not the case was air resistance. Galileo's theories were generally accepted.
Free fall is defines as "the motion of an object undergoing an acceleration of "g".
For objects in free fall you can replace acceleration with "g".
For projectile motion you have t take the vertical and horizontal components separately.
For the horizontal motion there horizontal motion is not affected by gravity or any other forces
so it acts as a constant speed. Therefore you can use speed equals distance divided by time.
If the object starts off at angle:
1. Resolve the initial velocity into vertical and horizontal components.
2. Use the vertical component to work out how high and long it is in the air for.
3. Use the horizontal component to work out how far it goes whilst it is in the air.
Terminal Velocity is when the force of weight is equal to the force of air resistance so there
is not net force and there is no acceleration.
Displacement time graphs.
The gradient of a displacement time graph tells you the velocity.
A curved displacement time graph means acceleration:
1. The greater the gradient of the curve the greater the acceleration.
2. The smaller the gradient the smaller the acceleration.

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Velocity time graphs.
The gradient of a velocity time graph tells you the acceleration.
The area under a speed time graph tells you the distance travelled.
Constant acceleration is shown by a straight line.
Decreasing acceleration if shown by a curve decreasing in gradient.
Increasing acceleration is shown by a curve increasing in gradient.
Mass, weight and centre of gravity.
Weight is equal to mass times the force of gravity.
Density is equal to mass divided by volume.…read more

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Work done is equal to the force causing motion times the distance moved. Work done is
measured in joules.
Power equals work done divided by time. Power is measured in Watts.
Power is also equal to force times velocity.
Conservation of energy principle is that energy can not be created or destroyed but energy
can be transferred from one form to another.
Some key equations are:
1. Kinetic energy is equal to half times mass times velocity squared.