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G481 Mechanics The equations
All the equations you need with definitions and units for OCR A Physics examination
19
Physics
12th Grade
05/14/2009

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Term

Define the symbols, units of measurement and limitations of the equation

 

Fx = F Cos θ

Fy = F Sin θ

Definition

F is the original force measured in N

Fx is the component of F in the horizontal direction

Fy is the component of F in the vertical direction

θ is the angle between the force vector F and the horizontal.

Term

Define the symbols, units of measurement and limitations of the equation

 

a=Δv/Δt

Definition

a is acceleration measured in ms-2

Δv is the change in velocity and is measured in ms-1

Δt is the change in time measured in seconds

Term

Define the symbols, units of measurement and limitations of the equation

 

v = u + at

Definition

v is the final velocity measured in ms-1

u is the initial velocity measured in ms-1

a is the constant acceleration in ms-2

t is the time taken measured in seconds

This equation only works if the acceleration is constant

Term

Define the symbols, units of measurement and limitations of the equation

 

s = 0.5(u + v)t

Definition

s is the distance moved in the direction of the acceleration measued in metres

v is the final velocity measured in ms-1

u is the initial velocity measured in ms-1

t is the time taken measured in seconds

The acceleration must be constant for this equation to work

Term

Define the symbols, units of measurement and limitations of the equation

 

v2 = u2 + 2as

Definition

s is the distance moved in the direction of the acceleration measued in metres

v is the final velocity measured in ms-1

u is the initial velocity measured in ms-1

a is the constant acceleration

The acceleration must be constant for this equation to work

Term

Define the symbols, units of measurement and limitations of the equation

 

F = ma

Definition

F is the resultant force (in Newtons) acting on an object of mass, m. (measured in kg) which causes the object to accelerate (measured in ms-2

If the object is moving very fast then the object mass will increase (relativistic effect) making this equation not work.

Term

Define the symbols, units of measurement and limitations of the equation

 

W = mg

Definition

W is the weight of an object measured in N

m is the mass of the object measured in kg

g is the gravitational field strength measured in ms-2 or Nkg-1

Term

Define the symbols, units of measurement and limitations of the equation

 

Moment = Fx

Definition

Moment is the turning effect of a force (F measured in N) on a pivotted object

x is the perpendicular distance between the force and the pivot

Term

Define the symbols, units of measurement and limitations of the equation

 

Torque

Definition

Two equal but opposite forces (both F) act an equal distance (d/2) from the pivot, one either side[image]of the pivot produce a torque

Term

Define the symbols, units of measurement and limitations of the equation

 

ρ = m/V

Definition

The density (ρ) of a material measured in kgm-3

is the mass (m) in kilograms divided by the volume (V) the mass occupies in m3.

Term

Define the symbols, units of measurement and limitations of the equation

 

P = F/A

Definition
P is the pressure acting on a surface measured in Nm-2 or Pa. (1 Pa = 1 Nm-2) due to a force ,F, measured in N acting on a surface area, A, measured in m2.
Term

Define the symbols, units of measurement and limitations of the equation

 

W = FxCosθ

Definition

W is the work done in Joules when a force, F, measured in N pushes an object a distance x.

The angle θ is the angle between the force and the direction moved

Term

Define the symbols, units of measurement and limitations of the equation

 

Ek = 0.5mv2

Definition

The kinetic energy of an object measured in joules is half the product of the objects mass,m, (measured in kg) and velocity in ms-1 squared.

If the object is moving very fast then the mass of the object will increase and the equation will not work.

Term

Define the symbols, units of measurement and limitations of the equation

 

Ep = mgh

Definition
The graviational potential energy, Ep, measured in Joules of an object is the product of its mass,m, (measured in kg), its height above the Earths surface,h, in metres and the grsavitational field strength,g, measured in Nkg-1 or ms-2.
Term

Define the symbols, units of measurement and limitations of the equation

 

F= kx

Definition

A force, F, measured in Newtons will cause an extension, x, (in metres) in a wire or spring of stiffness/force constant/spring constant, k, measured in Nm-1.

This equation only works for elastic springs and wires

Term

Define the symbols, units of measurement and limitations of the equation

 

E = 0.5Fx = 0.5kx2

Definition

Energy stored (measured in Joules) in a material under tension or compression, F,  (measured in Newtons)

x is the the extension of the material in metres and k is the force constant/spring constant/hooke's constant measured in Nm-1

These equations only work for elastic materials

Term

Define the symbols, units of measurement and limitations of the equation

 

stress = F/A

Definition

Stress is measured in Nm-2

Force acting through the material in Newtons

A is the cross sectional area of the material measured in m2.

Term

Define the symbols, units of measurement and limitations of the equation

 

Strain = x/L

Definition

Strain describes the change in shape of a material as a fraction

x is the extension of the material in metres

L is the original length of the material measured in metres.

Term

Define the symbols, units of measurement and limitations of the equation

 

Young Modulus = stress/strain

Definition

Youngs modulus describes the stiffness of a material in Nm-2.

Stress is the force ating perunit area through a material measured in Nm-2.

Strain describes how the shape of the ibject changes and has no units.

 

This equation only works for elastic materials

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