physics

Gravity attractive or repulsive?

Attractive always

Magnetism attractive or repulsive?

attractive and repulsive

Electrostatic attractive or repulsive?

attractive and repulsive

What is a contact force?

If two objects or materials need to be touching for the force to have an effect then it is a contact force.

eg - friction, air resistance

what is a non-contact force?

If two objects or materials do not need to be touching for the force to have an effect then it is a non-contact force.

eg - gravity, electrostatic, magnetic

what happens to the gravitational force as the mass of an object becomes larger and further away?

The larger the mass is, the greater the gravitational attraction. The further away a mass is, the less the gravitational attraction.

what do force diagrams show?

Force diagrams show you the direction a force is acting in.

The direction of the arrow shows you the direction of the force. The sizes of the arrows can be used to compare the sizes of the forces.

What is upthrust?

The upwards force on a body in a liquid or a gas

What is thrust?

A forward push

what is a reactive force?

A reaction force is a consequence of an action force which is opposite in direction.

What is mass?

Your mass is a measure of how many particles there are in your body. It does not matter where you are in the Universe, your mass does not change.

what is weig

what is the formula for force due to gravity?

Fg = mg

m = mass in kilograms

g = Earth’s gravitational field strength in N/kg = 9.8N/kg

what is newetons first law of motion?

If an object is stationary and an unbalanced force acts on it, it will start to move.

which direction does friction act and what do you get from it?

Friction always acts in the opposite direction to which an object is moving in.

Friction is a type of force.

Whenever you get friction between two objects you always get heat and wearing.

what is work?

• Work is the transfer in energy that occurs when a force moves an object in the direction of force

\n For example: The boy lifting weights, applies an upward force and the weights move up. When he holds the weights still, no work is being done. He is applying an upward force equal to the downward pull of gravity on each weight (but there is no movement in the direction of force).

what is energy?

• Energy is described as the capacity of an object or substance to do work (therefore it has the ability to make things move).

• The unit of energy is joule (J)

what are the two types of energy?

• There are two types of energy:

  • Potential (stored) energy

  • Kinetic (motion) energy

what is work the change of?

change in energy

what are the 4 types of potential energy?

• Elastic: (Or strain energy) is present in objects when they are stretched or compressed.

• Gravitational: present in objects in a position in which they could fall as a result of the force of gravity.

• Chemical: present in all substances as a result of the electrostatic forces holding atoms together.

• Nuclear: energy stored in the nucleus of all atoms.

what is the formula for gravitational potential energy?

Eg = mgh

Whereby Eg is gravitational potential energy (in J)

m is mass (in kg)

g is gravitational field strength (in N/kg) - 9.8 m/s2

Δh is the change in height or position (in m)

what is kinetic energy?

Kinetic energy is the energy possessed by an object due to its motion. Potential energy can be converted into kinetic energy (e.g. when the brick is dropped from a height, the brick in motion has kinetic energy).

what is the formula for kinetic energy?

Ek = ½mv2

Where Ek is the kinetic energy (in J)

m is the mass (in kg)

v is the velocity of an object (in m/s)

what is the efficiency of a system?

• The efficiency of a system is the fraction of energy supplied to a device that is useful energy (expressed as a percentage).

formula for efficiency?

efficiency = (useful energy output / energy input ) x 100%

useful energy = sum of kinetic, elastic and gravitational potential energy

what is a balanced force?

Balanced forces result in constant velocity / speed or remaining stationary

what is an unbalanced force?

Unbalanced forces result in accelerating or decelerating (negative acceleration)

what are scalar quantities?

quantities that are fully described by a number. (E.g. – mass, time, speed, distance)

what are vector quantities?

quantities that are fully described by both a number and a direction. (E.g. – displacement, velocity, acceleration, force)

what is the difference between distance and displacement?

• Distance (d) is a measure of the length of the path taken by an object. It is a scalar quantity.

• Displacement (s) is a measure of the change in position of an object. It is a vector quantity.

• In other words – the shortest path between two points

displacement = final position - initial position

what is speed?

• Speed (v) – Rate at which an object is moving.

• speed = distance / time

• v = d/t

• Like distance, speed does not depend on direction.

• Therefore it is a scalar quantity

what is velocity?

• Velocity (v) – speed with direction.

• velocity = displacement / time

• v = Δs / t

• Has magnitude and direction!

  • Magnitude (speed) – a measure that has a value

what is acceloration?

• Acceleration is the rate of change of velocity.

• A vector quantity, i.e. magnitude & direction.

formula for acceleration?

change in velocity/ time