Physics Definitions OCR A level

What six base units of the SI system are used in A Level Physics?

metre, kilogram, second, Ampere, Kelvin, Mole

What six base quantities of the SI system are used in A Level Physics?

length, mass, time, electric current, absolute temperature, amount of substance.

What is the value of the prefix T (tera)

10¹²

What is the value of the prefix G (giga)

10⁹

What is the value of the prefix M (mega)

10⁶

What is the value of the prefix k (kilo)

10³

What is the value of the prefix d (deci)

10⁻¹

What is the value of the prefix c (centi)

10⁻²

What is the value of the prefix m (milli)

10⁻³

What is the value of the prefix μ (micro)

10⁻⁶

What is the value of the prefix n (nano)

10⁻⁹

What is the value of the prefix p (pico)

10⁻¹²

What is the accuracy of measurements?

How close a measurements are to the true value.

What is the precision of measurements?

How close to each other repeated measurements are.

What is measurement error?

The difference between the measured value and the true value of the quantity.

What are random errors?

Measurement errors that occur due to results varying in an unpredictable way.

What is the main method for correcting for random errors?

Taking repeated measurements and finding the mean.

What are systematic errors?

A measurement error that causes the measurements to differ from the true value by a consistent amount for each measurement.

What is a zero error?

A systematic error that arises from an instrument reading reading a non-zero reading when nothing is being measured.

What is an absolute uncertainty?

The interval around the measured value within which the true value is expected to lie.

What is a percentage uncertainty?

The absolute uncertainty stated as a percentage of the measured value.

How do you combine uncertainties when measurements are added or subtracted?

Add together the absolute uncertainties.

How do you combine uncertainties when measurements are multiplied or divided?

Add together the percentage uncertainties.

What happens to the uncertainty in a measurement when it is raised to a power?

The percentage uncertainty is multiplied by the power.

What is a scalar quantity?

A quantity with magnitude but no direction.

What is a vector quantity?

A quantity with magnitude and direction.

When adding two perpendicular vectors what can you use to find the direction of the resultant?

Pythagoras' Theorem

When adding two perpendicular vectors what can you use to find the magnitude of the resultant?

Trigonometry

What is vector resolution?

The process of splitting a vector into two perpendicular components.

What is a resultant vector?

The sum of two or more individual vectors.

How is the resultant found in a vector diagram when adding several vectors together?

Join the vectors nose to tail and the resultant is from the tail of the first to the nose of the last vector.

What is displacement?

The distance of an object from a point in a specific direction (vector)

What is velocity?

Rate of change of displacement (vector) ∆s/∆t if constant

What is speed?

Change in distance traveled per unit time (scalar)

What is acceleration?

Rate of change of velocity (vector) ∆v/∆t if constant

What are the units of acceleration?

ms⁻²

What is meant by constant velocity?

Speed and direction of motion don't change

What is represented by the gradient of a distance-time graph?

Speed

What is represented by the gradient of a displacement-time graph?

Velocity

What is represented by the gradient of a velocity-time graph?

Acceleration

What is represented by the area under a velocity-time graph?

Change in displacement

What is represented by the area under an acceleration-time graph?

Change in velocity

When can the suvat equations by used?

When there is constant acceleration and motion along a straight line.

What is the effect of mass on the acceleration for an object in free-fall?

None

What is the relationship between displacement and time for an object falling freely from rest?

Displacement is proportional to time squared (sαt²)

What is a projectile

An object acted upon only by the force of gravity

What shape is the path of a projectile?

Parabolic

What is the initial vertical velocity of an object projected horizontally?

Zero

What angle of projection that results in maximum range

45°

Ignoring air resistance what is the acceleration of a projectile?

Always g downwards

How does horizontal velocity vary in projectile motion?

It is constant

If a projectile returns to its starting height

Initial and final velocities have the same magnitude

What equation used for the horizontal component of projectile motion?

Displacement = Velocity x time (since horizontal velocity is constant)

What aspect links the vertical and horizontal motion of a projectile

Time taken to fall

Why can SUVAT equations can be used for the vertical component of projectile motion

Since the motion is in a single direction with a constant acceleration

What is the vertical velocity at the peak of projectile motion?

Zero

What is the centre of mass of an object?

The point at which the weight can be assumed to act.

What does the weight of an object depend on?

It's mass and the gravitational field strength (W=mg)

What is a free-body diagram?

It is a diagram showing the set of forces acting on a single object.

What is weight?

The force due to gravity that acts through an objects centre of mass.

What is friction?

The force that acts between two surfaces in contact to oppose motion.

What is drag?

The resistive force that acts on an object moving through a fluid

What is tension?

The force within a stretched object such as a cable or rope.

What is upthrust?

The upward buoyant force that acts on an object in a fluid.

What is a normal contact force?

A force that acts perpendicular to a surface when an object rests on it.

How do you calculate the component of weight down a slope?

W sin (θ) where θ is the angle between the slope and horizontal.

How do you calculate the component of weight acting perpendicular to a slope?

W cos (θ) where θ is the angle between the slope and horizontal.

What are the key factors in determining the magnitude of drag force acting on an object in a fluid?

Speed and cross-sectional area

What is terminal velocity?

The maximum speed reached by a falling object when drag and weight are equal.

What is a moment?

The turning effect produced by a force.

What units do moments have?

Nm

How do you calculate a moment about a point?

Force x perpendicular distance to the line of action of the force

What is meant by a body being in equilibrium?

The net force and the net moment acting on the body are both zero.

What is the principle of moments?

For an object in rotational equilibrium the sum of the clockwise moments about any point is equal to the sum of anticlockwise moments about that point.

What is a couple?

A pair of equal and opposite forces acting on an object with different lines of action.

How do you calculate the moment of a couple?

Force x perpendicular distance between the lines of action of the forces.

What is a triangle of forces?

A vector diagram of the three forces acting on an object in equilibrium.

What is a resultant/net force?

The vector sum of forces acting on an object

What is the density of a substance?

mass per unit volume.

What are the units of density?

kgm⁻³

What is pressure?

Normal force acting per unit area

What is Archimedes principle?

The upthrust exerted on an object is equal to the weight of fluid displaced,

p = hg

What is work done equivalent to?

Energy Transferred

What are the SI base units equivalent to the Joule?

kgm²s⁻²

How is work done calculated?

W = F x cosΘ (distance moved x component of the force in the direction of motion)

What is Θ in W = F x cosΘ?

The angle between the force and motion.

What is energy?

The capacity of one object or system to do work (or cause a change) on another.

What is represented by the are under a force-distance graph?

Work done.

What is the principle of conservation of energy?

The energy of a closed system always remains constant. Energy can never be created or destroyed, only transferred.

What form of energy is due to the motion of a mass?

kinetic energy

What form of energy is due to the position of a mass in a gravitational field?

gravitational potential energy

What form of energy is due to the bonds between atoms in a substance?

chemical energy

What form of energy is due to the a reversible change in shape of an object?

elastic potential energy

What form of energy is due to the position of a charge in an electric field?

electrical potential energy

What form of energy is due to the forces between protons and neutrons in an atom?

Nuclear energy

What form of energy is due to electromagnetic waves?

Radiant energy

What form of energy is due to the mechanical wave motion of atoms?

Sound energy

What form of energy is due to randomly distributed potential and kinetic energies of the atoms within a system?

Thermal energy

What effect does friction have on the energy of a moving object?

Transfers kinetic energy primarily to thermal energy