1 Motion, forces and energy Flashcards
Common prefixes for units.
Prefix (symbol) Meaning
centi (c) ÷100
milli (m) ÷1000
kilo (k) ×1000
mega (M) ×1000000
giga (G) ×1000000000
Scalar
Is a physical quantity that has magnitude but no direction
E.g.Speed, volume, mass
Vector
Is a physical quantity that has both magnitude and direction.
E.g.Displacement, Velocity, acceleration, forces
Resultant force
The effect or result
Resolving Vectors
Shows the overall effect of the magnitude and direction of 2
or more vectors(Component vectors).
How to calculate a resultant vector
Using the “head to tail method”
Add the vectors to get the distance
To get the R.F. use geometry or Pythagorean theorem.
Speed
V = total distance travelled (m) ÷ total time taken (s)
Speed is a measurement of how far something travels in a unit of time.
Velocity is defined as speed in a given direction.
Acceleration
=change in velocity (m/s) ÷ time taken (s)
Acceleration is the change in velocity per unit time
Distance-time graphs
A straight, sloping line = constant speed
A straight, sloping line of higher gradient = faster constant speed
A flat/horizontal line = stationary (not moving).
Speed-time graphs and gradient
A flat horizontal line at zero speed = stationary
A flat horizontal line above zero speed = constant speed
An upward sloping line = accelerating; the steeper the gradient, the higher the acceleration
A downward sloping line = decelerating.
Gradient
increase in the y-axis ÷ increase in the x-axis
Gravity
9.8 m/s*2
Gravity
9.8 m/s*2
Terminal velocity
The top speed reached by any object experiencing air resistance or a similar resistance force.
Weight
Mass x gravity
Mass
Volume x Density
Density
Mass ÷ Volume
Why do things float in water?
They have a lower density
Force
Mass x acceleration
Force due to gravity(fg) is the same as
Mass due to gravity(mg)
Hooke’s law Is
Spring constant(K) = Force(F) ÷ Extension(x)
The force needed to stretch a spring or wire by one unit of length. Measured in N/m.
Circular motion
Force(F)=Mass x Velocity*2
÷ radius
Moment
Moment(T)= force x perpendicular distance to the pivot
A turning force.
The principle of moment
A system will not rotate if the clockwise and anti-clockwise moments are equal.
Centre of gravity
The imaginery point within an object that the mass and weight of the object is evenly dispersed around (also known as the centre of mass).
Elastic collision
Kinetic energy and there fore momentum is fully conserved.
Inelastic collision
Kinetic energy and there fore momentum is not conserved due to energy losses into other forms for example heat and sound.
Momentum
Momentum(P)= Mass(m) x Velocity(V)
Momentum is always conserved.
Impulse
Change of momentum(impulse)= Force(F) x Time in the collision.
What are the different types of energy stores
7
Kinetic
Gravitational potential
Thermal
Electrostatic/magnetic
Elastic potential
Sound
Chemical potential
Energy
Is the ability to work
What are the different types of energy transfers
Mechanical(force)
Electrostatic
Heating
Electromagnetic, sound or other waves
Conservation of energy
Energy cannot be eradicated or destroyed. It can only be transformed from one state to the other. Ek=Ep
Sankey diagram
Used to show energy transfers while also giving an indication of how much energy is transferred at each step.
Kinetic energy
1/2×mass (kg) × [velocity (m/s)]*2
The energy of moving objects.
Gravitational potential
mass (kg) × acceleration of gravity (m/s*2) × change in height (m)
Energy is stored when an object is raised to a height with in a gravitational field.
Work
W=Force x Distance
work done=energy transferred
Power
Power = Work ÷ Time
The rate at which work is done, or rate of energy transfer.
Boiler
Uses heat from the burning of fuels to boil water into steam.
Turbine
Transforms thermal energy from a fluid(liquid or gas) into rotated kinetic energy.
Generator
Consists of a coil/s of wire that rotate in a magnetic field to produce an electrical current.
Energy resources
Fossil fuels (coal, oil, gas)
Nuclear
Hydroelectric
Tidal
Wave
Solar
Wind
Geothermal
Energy efficiency
Efficiency(%)= (Useful energy÷Total energy) x 100
No energy transfer is 100% efficient.
Pressure
Pressure= Force ÷ Area
Pressure is a measure of force per area
Pressure in liquids
Pressure= Change in height X density(Pa) x gravitational field strength.
Conditions needed for equilibrium
No Resultant force
No Resultant moment
Air resistance
Consider a ball falling. Gravity pulls the ball downwards, but as the ball goes faster, air resistance acts upwards
KWH
energy transferred in one hour at a rate of transfer of 1 kW
