KEY EQUATIONS Flashcards
Average speed =
average speed = distance/time
V = d/t
Velocity =
Velocity = change in displacement/time taken
how to subtract a vector
to subtract a vector, add on the vector to be subtracted in the opposite direction
acceleration =
acceleration = gradient of velocity time graph
Displacement =
displacement = area under velocity time graph
The four equations of motion (Suvat)
V = u + at S = (u + v)/2 x t S = ut + 1/2 at² V² = u² + 2as
For a velocity v at an angle θ to the x-direction the components are:
x-direction: v cos θ
y-direction: v sin θ
In the absence of air resistance, an object has:
constant velocity horizontally and constant acceleration vertically.
Resultant force =
Resultant force = Mass x acceleration
F = ma
Weight =
Weight = Mass x acceleration of free fall W = mg
What do all physical quantities have
all physical quantities have a numerical magnitude (a numerical size) and a unit
What are base units in mechanics
length, mass, time, current and temperature are base units in mechanics
What on each side of a physics equation are the same`
base units on each side of a physics equation are the same
What should you do when you draw a scale drawing
when you draw a scale drawing you should:
State the scale used
draw a large diagram to reduce the uncertainty
What happens in a body is in equilibrium
if a body is in equilibrium, there is no resultant force and no resultant torque or moment about any point
When is work done
work is done on a body when a force moves (displaces) the body in the direction of the force.
Energy is then transferred from one body to another
work done =
Work done = force x distance
W = Fs
What does work done =
work done = energy transferred
Work done (angle)
Work done = Fs Cos θ
change in g.p.e =
Change in g.p.e = weight x change in height
ΔEp = mgΔh
Kinetic energy =
1/2 x mass x speed²
Ek = 1/2 mv ²
Efficiency =
efficiency = useful output energy/total input energy x 100%
power =
power = work done/ Time taken P = W/t
OR
Power = force x velocity P = F x v
Momentum =
Momentum = mass x velocity p = mv
what happens in a perfectly elastic collision
In a perfectly elastic collision of two bodies the relative speed of the body’s approach is equal to the relative speed of their separation
what happens during an inelastic collision
During an inelastic collision the total kinetic energy of the bodies becomes smaller
Resultant force is proportional to
Resultant force ∝ rate of change of momentum
F = Δp/Δt
Density =
density = mass/volume
P = m/v
pressure =
Pressure = normal force/cross-sectional area
P = F/A
Change in pressure =
change in pressure = density × acceleration due to gravity × depth
Δp= ρgh
upthrust =
upthrust = ρgV
= Weight of liquid displaced
Spring constant =
spring constant = force/extension
K = F/x
strain = extension/original length
strain = extension/original length
ε = x/L
stress =
Stress = normal force / cross-sectional area
σ= F/A
charge =
charge = current x time
ΔQ = IΔt
Energy transferred =
energy transferred = potential difference × charge
ΔW = VΔQ
resistance =
resistance = potential difference/current
R = v/I
Equations for power
Equations for power:
P = VI
P = I² R
P = V²/R
resistance =
Resistance = resistivity x length/cross sectional area
R = ρL/A
Resistivity =
resistivity = resistance x cross-sectional area / length
ρ = RA/L
Potential difference across a power source =
Potential difference across a power source =
V = E - Ir
Intensity =
intensity = power / area
What is intensity proportional to
intensity∝amplitude² or I∝A²
what does v (wave speed) equal to
v = fλ where v is the speed of the wave, f is the frequency and λ is the wavelength.
Doppler effect =
Doppler effect =
f0 = fs×v / (v±vs)
f0 is the observed frequency
Fs is the frequency of the source
v is the speed of the wave and vs is the speed of the source relative to the observer
Malus’s law:
Malus’s law
I = I0 cos² 0
The double slit equation
λ=ax/D
λ is the wavelength
a is the separation between the centres of the slits
X is the separation between the centres of adjacent bright or dark fringers
D is the distance between the slits and the screen
Determine wavelength λ with a diffraction grating
dsinθ=nλ
Wave speed (v) =
v = f λ
