# Physics Unit 1

My mindmap of the whole of OCR Physics A Unit 1.

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- Created by: Emily
- Created on: 17-04-13 11:52

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- Physics Unit 1
- Motion
- Physical Quantities and Units
- SI Units
- Mass - kg
- Length - m
- Time - s
- Temperature - K
- Current - A
- Amount of substance - mol

- Prefixes
- pico, nano, micro, milli, centi, kilo, mega, giga, tera
- -12, -9, -6, -3, -2, 3, 6, 9, 12
- p, n, µ, m, c, k, M, G, T

- SI Units
- Scalar and Vector
- Scalar - magnitude but not direction
- temperature
- speed
- Speed = distance per unit time
- Instantaneous speed - speed at a given instant of time

- time
- Constant Acceleration Equations
- displacement
- velocity
- Velocity - displacement per unit time

- acceleration
- Acceleration - rate of change of velocity
- (v - u) / t
- Free Fall
- g = 9.81ms-²
- Direct approach of measuring g
- Trap door and electromagnet method

- Indirect approach of measuring g
- Measuring the time taken for a pendulum to complete a full swing

- Direct approach of measuring g
- Affected by air resistance
- Acceleration of free fall is vertically down towards the centre of the earth

- g = 9.81ms-²
- Non-constant (non-linear) acceleration

- v = u + at
- s = ((u + v) / 2) x t
- s = ut + 1/2 a t²
- v² = u² + 2as

- Constant Acceleration Equations
- distance
- mass
- x or / by scalar gives a scalar

- Vector - magnitude and direction
- velocity
- Velocity - displacement per unit time

- displacement
- acceleration
- Acceleration - rate of change of velocity
- (v - u) / t
- Free Fall
- g = 9.81ms-²
- Direct approach of measuring g
- Trap door and electromagnet method

- Indirect approach of measuring g
- Measuring the time taken for a pendulum to complete a full swing

- Direct approach of measuring g
- Affected by air resistance
- Acceleration of free fall is vertically down towards the centre of the earth

- g = 9.81ms-²
- Non-constant (non-linear) acceleration

- force
- x or / a vector by a vector can give a vector or a scalar
- vector x scalar always gives a vector
- Vector calculations
- Vector is represented with an arrow
- Vector triangles are used to calculate the resultant of two vectors
- Pythagoras - a² = b² + c²
- Resolution of vectors
- vectors have a horizontal and vertical component
- horizontal = x sin angle
- vertical = x cos angle

- SohCahToa

- velocity

- Scalar - magnitude but not direction

- Physical Quantities and Units
- Forces in action
- Force
- Gravitational Force
- Between two objects with mass, e.g. weight
- Weight is the gravitational force on a body
- W = mg
- Centre of gravity
- Where the entire weight of an object can be considered to act as a single force.

- Magnetic Force
- Between two magnetic objects - the force between moving charges

- Electrical force
- Between chnarged objects - this is responsible for all interactions between objects
- Every object is made of positive protons and negative electrons which exert an electrical force on one another when they collide.
- e.g. Hand touching table

- Force causes acceleration, when an object has no resultant force, it has no acceleration
- Acceleration is proportional to force, if the mass is constant
- F = ma
- mass

- F = ma
- Acceleration is inversely proportional to mass, if the force is constant
- F = ma

- F = ma

- Acceleration is proportional to force, if the mass is constant
- Unit of force is the Newton (N)
- 1N is the force that causes a mass of 1kg to have an acceleration of 1ms every second

- Resistive force - drag
- Depends on - velocity, cross sectional area, roughness of surface, shape.
- Occurs when an object tvels through a fluid
- A fluid is a liquid or gas

- The drag on an object increases as it accelerates

- Equilibruim
- Zero resultant means zero acceleration for an object, and it is said to be in equilibruim
- An object moving at constant velocity is in equilibruim

- Gravitational Force
- Turning Forces
- Couple
- A pair of equal and parallel but opposite forces, which tends to produce rotation
- Resultant is always zero
- Torque
- torque = one of the forces x the perpendicular distance between the forces
- Describes the turning effect of a couple
- measures in Nm
- Produces a rotation rather than a linear motion. Describes items such as electrical drills

- Moment
- The moment of a force is the force x the perpendicular distance from a stated point
- The moment of a force is the turning effect of a single force
- Measured in Nm
- Principle of Moments
- For a body in rotational equilibrium, the sum of the clockwise moments equals the sum of the anticlockwise moments

- Couple
- Density
- ? = Mass per unit volume
- kg m3

- Pressure
- Force per unit area
- pressure = h?g at a depth in fluid
- Measured in Pascals (Pa)
- Floating
- Pressure on the bottom of an object keeps it afloat
- force upwards = weight downwards

- Cars
- work done by a vehicle against its braking force = force x distance
- Also called the kinetic energy of a vehicle

- stopping distance = thinking distance + braking distance
- Crumple Zones
- Parts of the car designed to collapse in a collision
- increase the distance over which the force is acting so the average force is less

- Seat Belts
- Increases the distance over which the force can act
- Airbags
- Keeps your mass in your seat to stop collisions with rigid objects

- Airbags
- Keeps your mass in your seat to stop collisions with rigid objects

- Increases the distance over which the force can act
- Airbags
- GPS
- Use trilateration to determine positioning of an object on the earth

- work done by a vehicle against its braking force = force x distance

- Force
- Work and Energy
- Work
- work = force = distance moved in the direction of the force
- Measured in Joules (J)
- 1J is the work done when a force of 1N moves its point of application 1m in the direction of the force

- Power is the rate of doing work
- Power
- measured in joules per second = watts (W)
- Kilowatt-hours (kWh)
- Equivalent to using 1000W of power for an hour.

- Power

- Energy
- The stored ability to do work
- Kinetic energy
- Where movement is taking place
- An object has speed
- Work an object can do by virtue of its speed
- kinetic energy = 1/2mv²
- Falling objects
- Gravitational Potential energy
- Where an object is at a high level in the Earth's gravitational field
- The energy stored in an object (the work an object can do) by virtue of its position in a gravitational field
- gravitational potential energy = mgh

- velocity of a falling object = Square root of 2gh

- Gravitational Potential energy

- Potential energy
- Fields where electric, magnetic, gravitational and nuclear forces exist.
- Gravitational Potential energy
- Where an object is at a high level in the Earth's gravitational field
- The energy stored in an object (the work an object can do) by virtue of its position in a gravitational field
- gravitational potential energy = mgh

- Conservation of energy
- Energy may be converted from one form into another, but it cannot be created or destroyed.

- Work
- Deformation of materials
- Elastic
- When it regains its original shape
- Once the elastic limit has been passed, the stretch becomes permanent
- Up to the elastic limit, the graph has a straight line
- Tension - Extension graph
- Graphs
- Past the elastic limit, the graph is a curve
- When it is permanently distorted

- The stretching of a wire

- Tension - Extension graph

- Up to the elastic limit, the graph has a straight line

- Plastic
- When it is permanently distorted

- Tensile Forces
- Forces that stretch objects such as wires.
- cause tension in the object
- Hooke's Law
- Elastic
- When it regains its original shape
- Once the elastic limit has been passed, the stretch becomes permanent
- Up to the elastic limit, the graph has a straight line
- Tension - Extension graph
- Graphs
- Past the elastic limit, the graph is a curve
- The stretching of a wire

- Tension - Extension graph

- Up to the elastic limit, the graph has a straight line

- The extension of an elastic body is proportional to the force that causes it
- F = kx where k is the force constant
- Elastic potential energy of the wire = 1/2kx²

- Elastic

- Compressive Forces
- Forces that squeeze an object

- Young modulus
- stress / strain
- stress is the force per cross sectiona area
- stress = F/A
- measured in pascals (Pa)

- strain is extension per unit length
- strain = x/L
- No units

- stress is the force per cross sectiona area
- The ratio between stress and strain

- stress / strain
- Categories of materials
- Ductile
- Can be drawn out into a wire - plastic deformation.
- takes a lot of strain before it breaks

- Brittle
- distort very little but will snap if subjected to large stress

- Polymetric
- such as rubber, doesn't break

- Ductile

- Elastic

- Motion
- Graphs
- Displacement - Time graphs
- Gradient - velocity

- Gradient - velocity
- Velocity - Time graphs
- Gradient - acceleration
- Area beneath - displacement

- Gradient - acceleration

- Displacement - Time graphs
- Constant Acceleration Equations
- v = u + at
- s = ((u + v) / 2) x t
- s = ut + 1/2 a t²
- v² = u² + 2as

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