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Forces and Energy Transfer.

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Forces and Energy Transfer

  • Speed=distance/time
  • Average Speed = average of 2 different speeds
  • Velocity = speed in a particular direction of travel.
  • Acceleration = increase in speed from stationary or a speed to its desired speed.
  • Acceleration is rate of change of speed
  • A = Change in speed/time taken: Therefore
  • A = v-u/t
  • V = final velocity
  • U = beginning velocity
  • Or: V2 = U2 + 2AS
  • OR: S = ut+ ½ at2
  • UNITS: M/S/S, M/S2, MS-2

Average Speed Equation:

V+U/2 = S(distance)/T

  • Equations of Motion:
  • ,
  • Scalar quantities, = magnitude only
  • Eg, Mass, Speed, Time
  • Vector quantities = magnitude and direction
  • EG, Weight, Acceleration, displacement
  • In a distance time graph, gradient = speed
  • In a speed time graph, the area under the graph is the distance
  • Acceleration on a velocity time graph is the gradient
  • Measured in Newtons
  • Show 2 things:direction and magnitude
  • Resultant of 2+ forces = single force that is equivalent to the combination.
  • Forces make objects: accelerate, decelerate and change direction
  • Objects resist a change in velocity
  • Size of acceleration is different for different objects
  • Amount of accel depends also on MASS IE:
  • Force (n) = mass(kg) + acceleration (m/s/s)
  • N2l
  • Find Vertical and Horizontal component of vel
  • Vertically use EQNS of motion
  • 3. Horiz usE S = d/t


  • For every action there is an equal and opposite reaction
  • For instance when you kcik a football, the football kicks you back as such
  • Why is it a bad idea to drive into a concrete post at 70 KPH?
  • According to Newtons 3rd law the block will apply the same force on the car as the car applies on the block. Except the block is probably buried in cement, so it would remain still but the car would continue, or try to continue, to go forward unless braking forces were applied, so the car would go straight into the block and the car would crumple.
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  • Most materials will change shape when a small force is applied to them but will return to their original shape when then force is released.
  • Materials which do this  = elastic
  • Not = plastic
  • If we apply a load to a spring tiw ill extend, more we apply more it will extend
  • When we remove, the load the spring retirns to its original length
  • But if we apply to much, the spring will be damaged and willl not return, it is passed it’s ELASTIC LIMIT.
  • Robert Jooke, fount extension is proportional to load provided el not exceeded = Hooke’s Law
  • Can’t be created, just reused
  • Changes from 1 type to another e.g. Kinetic to Heat
  • Principle of Conservation of energy Energy exists in different forms and can transfer between them. Everything need energy
  • Different forms
  • Fuels store chemical energy
  • People and machines can convert this energy into other forms to allow them to do useful tasks.
  • Energy us never lost or destroyed
  • Always converted
  • Forms of energy:
  • Kinetic
  • Heat
  • Chemical
  • Electrical
  • Light
  • Sound
  • Gravitational Potential Energy
  • Energy:  Different Forms
  • Conserved
  • Required to do useful things

Potential Energy is affected by gravity, mass and height

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PV/t = const

Turning effect of a force dpends on the size of the forace and the perpendicular distance from the point of application to the pivot.

Moment = Force x distance

Sum of clockwise moments = sum of anti-clockwise moments.

  • Resistors get hot when electric current passes through them
  • Voltmeters placed in parallel ammeters in series
  • V = IR
  • Current is a flow of charge
  • It Transfers energy to the different components within the circuit
  • We control current by adding or removing obstructions
  • Resistance = V/I
  • Ohm’s law states that current through a wire is directly proportional to the voltage across it unless temperature is not constant
  • Bulb doe not obey Ohms Law its VI graph is not a straight line because as current increases the temperature changes
  • P = VxI
  • I = Q/t
  • V = E/Q
  • R = V/I
  • P = VI
  • P = E/T
  • I = a
  • Q = c
  • T = s
  • V = v
  • P = w
  • E = J
  • R = Ohms
  • Thermistor reduces resistance as temperature increases

Electrical Power is the rate of energy transfer in Watts

P = E/t

Or P = Current x P.D

Also IxV

E = VxIxT

Prove that P = VxI

P = E/T

P = Vq/(Q/I)

So P = VI

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