# Physics Unit 1 revision

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## Interpreting graphs of motion

Displacement-Time Graph

Gradient of the graph is velocity.

Velocity-Time Graph

Gradient of the graph is acceleration.

Area under the graph is displacement.

Acceleration-Time Graph

Area under the graph is velocity.

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## Units

SpeedDistance/Time = ms-1

Acceleration- Change in velocity/Time = ms-2

Force- Mass X Acceleration= Newton. Kgms-2

Pressure- Force/Area = pascal (Pa). Kgm-1s-2

Work- Force X Distance = Jouke. Kgm2s-2

Power- Work/ Time = Watt . Kgm2s-3

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## Equations of motion

The 3 equations of motion are:

v = u + at

v2 = u2 + 2as

s = ut + 1/2at2

v = final velocity

u = initial velocity

a = acceleration

t = time

s = displacement

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## Material definitions

Plastic: will remain deformed

Hard: Difficult to indent

Stiff: high young modulus

Tough: high energy density/ large plastic region/ able to absorb energy

Brittle: an object will shatter when subject to shocks, without deforming plastically.

Strong: high breaking stress/ can withstand large forces before it breaks

Malleable: hammered into thin sheets

Ductile: Can be drawn into wires without losing their strength

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## Stress, Strain, Young Modulus etc

Hookes Law= up to a given load, the extension of a pring is directly proportional to the force applied to the spring. F= KX  (k-spring constant)

Limit of proportionality- the point the material  stops obeying hooks law. but would still return to its original shape if stress is removed.

Elastic limit- at this point the material starts to behave plastically.  at this point the material would no longer return to its original shape once the stress was removed.

Yield  point- the stress at which a large amont of plastic deformation takes place with a constant or reduced load.

Work done= 1/2 X Max force X extention

Elastic strain energy= the area under the graph.

Stress=Force/Cross sectional area

Strain=Extension/ original length

Young modulus= stress/strain.

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## Tensile strain and stress

Tensile strength: The tensile stress at which a material fails.

Tensile force: The tensile force required to stretch a material.

Tensile stress: The tensile force per unit cross-secitonal area.

Tensile strain: The extension per unit length.

Strength: A materials ability to withstand stress.

Stiffness: A material which resists tensile force.

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## Fluids

Density=  Mass/Volume

Upthrust= a consequence of water pressre being greater below an immersed obect

Upthrust= weight displaced = vpg

an object willfloat in a fluid if the upthrust is equal to its weight

laminar flow=no abrupt change in velocity or direction of flow lines. adjacent layersdo not cross  over each other

turbulent= streamlines are no longer continuous

viscosity= the resistance of a fluid to flow

Resultant force= W-(U+F) If an object is accelerating downwards

viscous drag increases untill (u+f)= w << terminal velocity.

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