GCSE Physics- Crucial Definitions Flashcards
Vector quantity
A quantity which is defined by three things, a magnitude, a direction and a unit
Scalar quantity
A quantity which is defined by two things, Magnitude and unit.
State Newtons 1st law.
The forces on a system are balanced therefore Fr=0, the object will not accelerate.
The object has two possible states of motion;
•Stationary
•Moving at a constant velocity.
State Newtons 2nd law.
Fr=m a, and so Fr/m=a; the acceleration, a of a body is directly proportional to the resultant force,Fr, and inversely proportional to the mass, m
What is mass
Is a measure for the amount of matter of an object
What is weight
Is the size of the gravitational force of an object
What is density
Density is the mass per unit volume d=m/V
State Hooke’s Law
The extension of a spring is directly proportional to the applied force up to the limit of proportionality
What is pressure
The force per unit area
What is conservation of energy?
Energy cannot be created or destroyed, merely transferred from one to the other.
What is efficiency
Efficiency is the ratio of useful energy out/total energy in. It is a measure of effectiveness of a device at transferring energy into a desired form.
What is power?
Power is the rate of doing work or the rate if transferring energy.
What is a moment?
A moment is the product of force (F) multiplied by the perpendicular distance (d).
State the principle of moments.
For a system in rotational equilibrium the sum of the clockwise moments=Sum of anti-clockwise moments about any point (or the pivot point).
What is the centre of mass?
The point which through the entire mass of the object appears to be concentrated.
What is the centre of gravity?
The point through which the entire weight of an object appears to act.
What is an Atomic mass number?
The number of protons and neutrons in an atom.
What is an atomic number
The number of protons in an atom.
What is ionisation?
The process by which an atom or molecule acquires a negative or positive charge by losing or gaining electrons or form ions.
What is an isotope
Variants of the same element with the same number of protons but different number of neutrons.
What is a half life?
The average time taken for the number of radioactive nuclei to reach half its initial value,or the average time taken for the activity of a radioactive source to reach half its initial value.
What is activity of a source?
The number of disintegrations per second of a source.
What is background radiation?
Radiation that takes place naturally and is caused by radioactive material in rocks, the air and our bodies and partly by cosmic rays from outer space.
