Physics exam revision Flashcards
Revise on basic knowledge coming up on exam after half term
What is displacement?
Is a distance in a given direction
What is a vector?
Is a physical quantity that has a magnitude and a direction. e.g: force, acceleration, and velocity.
What is a scaler?
A physical quantity which has only a magnitude but no direction. e.g: Energy, time and mass.
What is a force?
A force is a push or a pull that acts on an object because of its interaction with another object.
What is a contact force?
A contact force is when two objects interact with each other by touching. e.g: air resistance, tension and normal contact forces.
What is a non contact force?
A force that interacts with another object at a distance. e.g : gravitational force, magnetic force and electrostatic force.
What is Newton’s third law of motion?
When two objects interact with each other they exert an equal amount of force on each other.
What is a resultant force?
Total amount of force acting on an object.
What do we say when the resultant force is zero?
The forces acting on the object are balanced.
What is Newton’s first law of motion?
if the forces acting on the object are balanced:
1. if the object is at rest it stays stationary
2. if the object is moving it keeps moving with the same speed and in the same direction.
If only 2 forces act on each other with zero resultant force, the forces must be equal to each other and act in opposite directions.
If an object is acted on by two unequal forces acting in opposite directions the resultant force is:
- Equal to the difference between the two forces
- Moves in direction of the larger force
If two forces act in the same direction the resultant force is:
The sum of the two forces and is in the same direction.
What is a moment?
The turning effect of force on an object.
What’s the formula for moment?
M = F x D
What are force multipliers?
Using something to move a load which is much larger compared to the effort being put in.
The moment of force can be increased by:
- Increasing the size of the force
- Increasing the distance between the pivot and the point of force.
What is the use of the lever?
The lever is used to increase the size of a force acting on an object.
What is the use of the gear?
To transmit the rotational effect of a force.
If an object is balanced:
Sum of anticlockwise moments about the pivot = sum of clockwise moments about that pivot.
Formula for moments and equilibrium.
W1 x d1 = W2 x d2
Why are substances radioactive?
Substances which are radioactive have unstable nucleuses and becomes stable or less stable by emitting alpha, beta or gamma radiation.
What is alpha radiation and its relative charge?
Its two protons and two neutrons and has a relative charge of +2
What is beta radiation and what is its relative charge?
Its fast moving electrons and has a relative charge of -1
What is gamma radiation and what’s it’s relative charge?
It is electromagnetic radiation and has no charge.
What is radioactive decay?
An unstable nucleus becomes more stable by emitting an alpha, beta or gamma particle.
When an unstable nucleus emits an alpha particle:
- Its atomic number goes down by two, and its mass number goes down by four.
- The mass and the charge of the nucleus are both reduced.
Why are beta particles emitted?
A beta particle is an electron created and emitted by a nucleus that has too many neutrons compared with its protons.
When an unstable nucleus emits a beta particle:
- The atomic number of the nucleus goes up by 1, and its mass number is unchanged( because neutron changes into a proton.)
- The charge of the nucleus is increased and the mass if the nucleus is unchanged.
When an unstable nucleus emits a gamma particle:
A ray of electromagnetic radiation is released. Neutron emission can occur as a result of alpha colliding with unstable nuclei in the substance. Such a collision can cause the nuclei to become even more unstable and emit a neutron. Because the emitted neutrons are uncharged they can pass through substances more than an alpha and b particle can.
What can be used to measure a substances radioactivity?
A Geiger counter
Why is radioactive substances dangerous?
- The radiation can knock electrons out of atoms. The atoms become charged because they lose electrons. This process is called ionisation. When an object is exposed to ionisation it is said to be irradiated but it does not become radioactive.
- Radioactive contamination - unwanted presence of material containing radioactive atoms on other materials.
Workers who use ionising radiation by:
- Keeping as far away as possible from the source of radiation.
- Spending as little time as possible in at-risk areas.
- Sheilding themselves by staying behind thick concrete barriers or lead plates.
