Physics recall test pt 1

Independent variable, Dependant variable and control variable

Independent variable = the thing you change in an investigation, dependant variable = the thing you measure in an investigation, control variables = anything you keep constant in an investigation.

Resolution

The resolution of a piece of equipment is the smallest value the equipment can read to e.g. a ruler can read to 1mm

Uncertainty in means

The uncertainty in a mean result gives you the range of values that you expect the true value to lie between.

How to find uncertainty

To find uncertainty, you need to repeat your investigation. Uncertainty = ½ range of your repeated results

reason for repeating results

to look for anomalies and reduce the impact of random errors

Dataloggers attached to probes are better than normal lab equipment because:

The resolution is better, It reduces the chance of human error, You can take many results in quick succession and You can take results over a long period of time e.g. over night

Scalar and vector quantities

A scalar quantity has a magnitude (size) only, a vector quantity has a magnitude and direction.

Scalar examples

Distance travelled, speed, mass, time, energy

Vector examples

Displacement, velocity, any force, acceleration, Momentum

Contact and non contact forces

Contact forces: friction, normal contact force, air resistance and tension. Non-contact forces: weight/gravitational force, magnetic force, electrostatic force between charged particles.

Weight definition

Weight is the force acting on an object due to gravity. DO NOT CALL IT GRAVITY. It depends on the gravitational field strength and mass of the object and acts from the “centre of mass”

Newtons First Law

An object will remain at rest, or in constant motion, unless acted upon by a resultant force

Inertia

The tendency of objects to continue in their state of rest or of uniform motion

Newtons Second Law

acceleration is directly proportional to resultant force and inversely proportional to mas

Inertial mass

a measure of how difficult it is to change the velocity of an object, it is defined as the ratio of force over acceleration

Newtons Third Law

If object A puts a force on object B, object B will put an equal and opposite force on object A.

Stretching an object

If you want to stretch, bend or squash an object, you need more than one force (one to hold it in place), otherwise the object will just accelerate; stretching an object stores elastic potential energy.

Stretching force

The stretching force applied to an object is directly proportional to the extension

Elastic and inelastic materials

Elastic materials will return to their original shape after the deforming force is removed, inelastic materials will not (they are permanently deformed)

Distance and Displacement

Distance (scalar) is how far an object moves, displacement (vector) is how far an object moves overall from start to finish in a straight line with the direction

Speed and Velocity

Speed (scalar) is how fast an object is going, velocity (vector) is the speed with direction.

Typical speeds

Walking - 1.5m/s, Running – 3m/s, Cycling – 6m/s, Sound in air – 330m/s

The gradient of a distance-time graph

Speed

The gradient of a velocity-time graph + the area under it

The gradient of a velocity-time graph is the acceleration, the area under the graph is the distance travelled.

A system

a group of objects that interact.

Energy stores

Kinetic, Gravitational potential, Elastic potential, Nuclear, Chemical, Internal (sometimes called Thermal), Magnetic

Energy transfers

Via Heat (radiation), Via Sound (radiation), Via Light (radiation), Electrically, Mechanically (by forces)

Conservation of energy

The total energy of a system remains constant so energy cannot be created or destroyed; it can only be transferred between stores.

Efficiency

a measurement of how much useful energy comes out of a device, compared to how much energy went in

Energy unit

Energy is measured in Joules (J)