# Unit 4 Physics Summary Flashcards

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• Created by: LZ95
• Created on: 02-04-14 21:19
What is Newton's first law of motion?
Object remains at rest/uniform motion unless acted on by a force
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What is Newton's second law of motion?
Rate of change of momentum of an object is proportional to the resultant force on it.
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What does the area under a force time graph represent?
Change of momentum/impulse of the force
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What is Newton's third law of motion?
When two objects interact, they exert an equal + opposite force on each other.
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What is the principle of conservation of momentum?
The total momentum remains constant provided no external resultant force acts on the system.
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What is an elastic collision?
When there is no loss of energy
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What is a totally inelastic collision?
When the colliding objects stick together
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What is a partially inelastic collision?
When colliding objects move apart and have less kinetic energy after the coll
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What is the centripetal force on a hill?
mg - S = mv^2/r (where S is support force)
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What is the centripetal force on a roundabout?
mv^2/r (due to friction)
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When is there no sideways friction on a banked track?
When v^2=grtan(x)
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What is the centripetal force on the Big Dipper?
S - mg = mv^2/r
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What is the definition of simple harmonic motion?
Oscillating motion in which the acceleration is: -proportional to the displacement; -in the opposite direction to the displacement
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Frequency of oscillation of a loaded spring is decreased by what?
Adding extra mass and using weaker springs
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What does a freely oscillating object do?
It oscillated with constant amplitude because there's no friction acting on it
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What does light damping do?
It decreases the amplitude gradually by the same amount each cycle.
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What does critical damping mean?
The damping is just enough to stop the system oscillating after it has been displaced and released from equilibrium
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What does heavy damping mean?
The damping is so strong that displaced object returns to equilibrium much more slowly and no oscillating motion occurs.
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What happens as the frequency approaches the frequency of the mass spring system?
1. The amplitude of oscillations of the object continually increases. 2. The phase difference between displacement and periodic force increases from 0 to pi/2 at natural frequency.
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What happens at resonance?
The applied frequency = the natural frequency
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Define gravitational field strength
Force per unit mass of an object placed in the field
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Define gravitational potential
At a point in a gravitational field is the work done per unit mass to move a small object from infinity to that point
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What are equipotentials?
Lines of constant potential
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What is the potential gradient at a point in a gravitational field?
It is the change of potential per metre at that point
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What must be done to the gpe to move a mass a small distance in the opposite direction to the gravitational force?
It must be increased by: - an equal and opposite force acting through the distance; -an amount of energy equal to work done
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What do Newton's laws of gravitation assume about the gravitational force between two point objects?
1. The force is always an attractive force. 2. It is proportional to the mass of the object. 3. It is proportional to 1/r^2
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What is Kelper's third law?
r^3/T^2 is constant
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What is a geostationary orbit?
An orbit that stays in one relative position above the earth (directly above the equator) and has a time period of 24 hours.
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What is a polar orbit?
An orbit which is lower than a geostationary orbit and covers a large proportion of the Earth's surface
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Name some uses for both polar and geostationary orbits
Polar orbits: Can be used to track weather, used for spying, photography of the earth; Geostationary orbit: can be used for satellites, TVs, mobile phones
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What makes something an electrical conductor?
It contains lots of free electrons which move about and are not attached to any one atom.
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What makes something an insulating material?
It does not contain free electrons as they are all attached to individual atoms.
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Define electric field strength
It is the force per unit charge on a positive test charge placed at that point.
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What is a point charge?
A charged object in a situation where distances under consideration are much greater than the size of the object.
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What is the capacitance of a capacitor?
Charge stored per unit pd.
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What is the time constant (RC)?
The time taken to reach 63% of the final charge.
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What is the motor effect?
The force on a current-carrying conductor due to a magnetic field.
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In which direction do magnets work?
North to South
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Where does the force of a magnetic field on a moving charged object act?
At right angles to the direction of motion
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Why is there no work done by the magnetic field?
As the force always acts at right angles to the velocity of the particle
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What does the force cause and why?
Centripetal acceleration as it is perpendicular to the velocity.
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What causes radius 'r' of a circular orbit of a particle in a magnetic field to decrease?
1. An increase in B (flux density) 2. A decrease in v 3. if the particles have a larger specific charge (Q/m)
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What is electromagnetic induction?
When a wire cuts across the lines of a magnetic field.
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What can induced emf be increased by?
1. Moving the wire faster; 2. Using a stronger magnet; 3. Making the wire into a coil
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What is Lenz's law?
The direction of the induced current is always such as to oppose the change that causes the current.
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The induced emf in a circuit is equal to the rate of change of flux linkage through the circuit.
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Why is the induced emf referred to as the back emf?
As it acts against the p.d.
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Name a transformer equation
Electrical power supplied to primary coil = electrical power supplied by secondary coil
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Why is gravitational potential negative?
As the force between two mass is always attractive and it is impossible to have a negative mass
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## Other cards in this set

### Card 2

#### Front

What is Newton's second law of motion?

#### Back

Rate of change of momentum of an object is proportional to the resultant force on it.

### Card 3

#### Front

What does the area under a force time graph represent?

### Card 4

#### Front

What is Newton's third law of motion?

### Card 5

#### Front

What is the principle of conservation of momentum?