Physics Notes: Work, GPE and Power
Work and Power -The amount of energy used to move something a certain distance.-Work (Joules/J) = Force (Newtons/N) x Distance Moved (Metres/m) -W = F x D -E.g, You use 20 newtons of force to carry a crate 10m, 20x10=200J Gravitational Potential Energy (GPE) -Energy associated with height above the ground. Work done in lifting a mass a vertical height.-GPE (Joules/J) = Mass(kg) x Gravity(10N/kg) x Height(m) -GPE = m x g x h -E.g, GPE at top of a 10m diving board. 70Kg x 10N/Kg x 10m = 700J Power -Power = The rate at which work is done -Power(Watts) = Work(Joules)/Time(Seconds) -P = e/t -Lift a weight of 100N a distance of 0.5m in 2s… 100N x 0.5s = 50J, 50/2 = 25W Speeding up Speed -Speed(m/s) = Distance(m)/Time(s) -E.g, walk 20m in 5s, 20/5 = 4m/s Acceleration -Acceleration(m/s^2) = Change in velocity(m/s)/time taken(s) -a = (v-u)/t -E.g, 0-60 m/s in 3.5s = 60/3.5 = 17.143m/s^2 1 / 3
Forces Force -Force(Newtons/N) = Mass(Kg) x Acceleration(m/s) -F = ma Weight -Weight is the force of gravity on an object -Weight(Newtons/N) = Mass(kg) x Gravitational Field strength(10 on Earth) -E.g if I have a 70kg mass, I weigh 700N -When an object falls, weight pulls it down but air resistance opposes this. When air resistance is equal to the weight of the object, it reaches a constant velocity and its acceleration is 0 (terminal velocity) -A vector quantity has magnitude and direction, a scalar has only magnitude
-Thinking distance factors:
-Drugs/Alcohol -fatigue -distractions
-Breaking distance factors:
-Wet or icy roads -bad quality tires -car mass -Stopping Distance = Breaking Distance + Thinking Distance 2 / 3
Waves and The Electromagnetic Spectrum -Longitudinal waves, oscillations of waves are parallel to energy flow - Sound -Transverse waves, oscillations of waves are perpendicular to energy flow - Light, water
-Definitions:
-Amplitude: Distance between centre line and top/bottom of wave (volume in sound) -Frequency: Number of oscillations for a certain time period. Formula = f=1/T e.g, if 1 oscillation takes 0.5s, 1/0.5 = 2. Frequency = 2Hz (Hertz - times per second)
-Wavelength: Distance between two crests or troughs of a wave.
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-Period of a wave: The time it takes for 1 cycle (1 wave)
-Wave speed = frequency x wavelength: v = f x (lambda)
-Doppler Effect:
-When a wave changes in frequency due to movement.-E.g, When a car zooms past you, note of its sound decreases as it passes you.-This is because it is either catching up to its own sound waves, or moving away from them.-Happens in Light and Sound. In light, when things move away they are redshifted, when they move towards you they are blue shifted -All waves can be reflected and refracted
-Light Spectrum (low to high wave length):
-radio - communication, microwaves - cooking, infrared - heaters, visible - optical fibres/photography, ultraviolet - fluorescent lamps, x rays - observing internal structure of objects, gamma rays - sterilisation
-Dangers:
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