physics

unit 3 and 4

what is a vector?

quantity that has magnitude and direction; represented with arrow or tilda (~)

what is the resultant vector?

result of two or more vectors combined, either through vector addition or subtraction

how to resolve vectors into components?

1. resolve each vector into their horizontal and vertical components (v1 x and y, and v2 x and y)

2. if two vectors are in different directions, put head to tail and find the net vector of horizontal and vertical directions (vx = v1x + v2x; vy = v1y + v2y)

3. find magnitude and direction using tan

4. bearing or compass in correct quadrats with direction

what are the horizontal and vertical components of velocity?

independent components of each other; resolution of a projectile’s velocity in the horizontal or vertical direction

what is initial velocity’s components?

ux = u cos θ, uy = u sin θ

what happens at maximum height?

vy = 0

what is final impact in projectile motion?

vx and vy (convert final velocity components into magnitude and direction)

what are complementary angles?

those that add up to 90 degrees e.g 60 and 30; projectile released at ground level will achieve maximum range at 45 degrees

what is applied force (Fa)?

force applied to an object by a person or another object on a flat surface; Fv = FA sin θ, Fh = Fa cos θ

what is weight?

force of gravity acting on an object; Fg = mg

how to get parallel (to surface) force?

Fp = Fg sin θ

how to get perpendicular (to surface) force?

Fperpendicular = Fg cos θ

what is the normal force for an object at rest on horizontal surface with no other forces acting?

Fn = -Fg

what is the tension force for a hanging object at rest?

Ft = Fg

what is the net force for an object moving on flat surface in horizontal direction?

Fnet = Fh (Fa cos θ) + Ff

what is the net force for a hanging object moving in vertical direction?

Fnet = Ft + Fg

what is the normal force for an object being pulled on flat surface?

Fn = Fg - Fv

what is the normal force for an object being pushed on flat surface?

Fn = Fg + Fv

what is the frictional force for an object on flat surface?

rearrange Fnet = Fh + Ff

what happens when an object is at rest or travelling at constant speed on flat surface?

Ff = Fh (same in magnitude but opposite direction)

what is the net force for an object sliding down incline with no friction?

Fnet = Fp

what is the net force for an object sliding down incline with friction?

Fnet = Fp - Ff

what is the net force for an object pulled up incline with no friction?

Fnet = Ft - Fp (but if constant speed, Fnet = 0 therefore Ft = Fp)

what is the down the incline force for an object pulled up incline with friction using a hanging mass?

Fdown = Fp + Ff

what is the equation for hanging mass up the slope?

m2g - Fup = m2a

what is the equation for overall mass on the slope?

Fup - Fp - Ff = m1a

what is uniform circular motion?

motion of an object travelling at a constant speed in circle due to a force that acts on the object in a direction perpendicular to the velocity of the object

what is a revolution?

circular motion of an object around another

what is a rotation?

circular motion of an object around its own axis

what is centripetal force?

force acting on an object travelling with uniform circular motion that pushes or pulls object towards centre of motion (Fc)

what is centripetal acceleration?

acceleration experienced by an object moving in a circular path towards centre of motion

what is a period in circular motion?

time taken for an object to complete one revolution around centre of motion

what is tangential velocity?

linear velocity of an object undergoing circular motion where the magnitude is the speed of the object and the direction is a tangent to circular path of motion

what is rotational speed?

number of revolutions an object does per second

what is average speed in circular motion?

The total distance traveled by an object divided by the total time taken to cover that distance

how to calculate a period in circular motion?

T = time/number of revolutions

what is gravity?

force of attraction between objects with a mass

what is newtons law of universal gravitation?

force of attraction between each pair of point particles is directly proportional to product of their masses and inversely proportional to square of distance between them → Fg = GMm/r² (m/M is masses of objects)

what is a gravitational field?

region of space surrounding a body in which another body experiences a force of gravitational attraction

what are the units for gravitational force?

radial distance = m

G = N m² kg^-22

mass = kg

what is gravitational field strength (g)?

net force (F) per unit mass (m) at a particular point in gravitational field

what are the units for gravitational field strength?

N/kg

what is keplers first law of planetary motion?

law of orbits - all planets move about the sun in elliptical orbits. having the sun as one of their foci

what is keplers second law of planetary motion?

law of areas - a radius vector joining any planet to the sun sweeps out in equal areas at equal lengths of time

what is keplers third law of planetary motion?

harmonic law/law of periods - square of sidereal period of a planet is directly proportional to the cube of its mean distance from the sun

→ T² is directly proportional to r³ (radius of orbit)

what is the formula of kepler and newtons third laws combined?

gravitational force = centripetal force, so Fg = Fc where T²/r³=4pi²/GM

what is coulomb’s law?

states that like charges repel and opposite charges attract, with a force proportional to the product of electric charges and inversely proportional to the square of the distance between them (1.6×10^-19 J)

what is coulomb’s law expressed as?

F = (coulomb constant) x Qq/r² where r is radial distance in m, Q and q is charge in coulombs

what is the appropriate notation for coulomb’s law problems?

Fab = force acting on A due to B (positive to negative)

what is an electric field?

region of space in which an electrified object will experience a force due to presence of electric charges

what is electric field strength?

intensity of an electric field at a particular location in that field; measure of force acting on a unit charge (q) placed at that point in the field

what is the formula for electric field strength?

E=f/q or E= k x q/r²

when will electric field strength be 0?

when Ea = Eb

what is electric potential energy?

capacity of electric charge carriers to do work due to their position in the field

what is a uniform electric field?

has a constant field strength and found between charged parallel plates

in a uniform electric field, if an electron is projected into it, which direction will it go?

towards the positively charged plate in a curved path (as it is negatively charged; attraction)

what is a magnetic field?

a region of space where a magnetic force is experienced

how to represent magnetic field lines?

• drawn from north to south pole

• more dense and closer together = stronger

how to represent magnetic field lines into or out of the page?

out of: circle with dot inside; into: circle with cross inside

what can a moving electric charge generate?

a magnetic field; electric fields can accelerate both moving and stationary charged particles but a charge MUST be moving for a magnetic field to influence it

how can magnetic field strength be represented visually?

flux lines being closer (stronger) or further apart (weaker)

what is the unit for magnetic field strength?

tesla (T); 1T = 1 NC/ms

how to determine the magnitude of magnetic field in current carrying wire?

B= magnetic permeability constant x I/r Teslas

how to determine direction for current carrying wires?

using the right hand rule, where your thumb points in direction of current and fingers wrap around magnetic field (into the page is away from you (clockwise), out of the page is towards you (anticlockwise), etc)

how to determine the magentic field strength in a solenoid?

B= permeability constant x nI where n is the number of turns per unit length.

how to determine n (number of turns per length)?

n = N/L where N is number of turns and L is length of solenoid

what is a solenoid?

long straight coil/coils of wire used to generate a controlled and almost uniform magnetic field

how to determine north pole of solenoid?

the north pole of a solenoid can be determined by using the right-hand rule: if you curl the fingers of your right hand in the direction of the current flow (how the wires turn) through the solenoid, your thumb will point toward the north pole.

which way does current flow in a solenoid?

positive terminal of battery to negative terminal (from diagram); convectional current

what is conventional current?

the flow of electric charge defined as moving from the positive to the negative terminal, contrary to the actual flow of electrons

how to determine the magnitude of MFS at a point at an angle to two perpendicular current carrying wires?

• find MFS at point P due to A and at point P due to B (direction is perpendicular to current carrying wire/s)

• use vector resolution (fore direction: redraw vectors head-to-tail)

how to determine the magnitude of MFS at a point between two current carrying wires?

find MFS of both and use vector addition

what happens if charged particle/current carrying wire is moving in magnetic field?

they experience a force

how to determine the magnitude of a force experienced by a wire in magnetic field?

F = BIL sinθ where θ is the angle between the direction of the magnetic field and the current

what happens if the current carrying wire/charged particles is perpendicular to magnetic field (90 degrees)?

F is at its maximum, sin θ = 1

what happens if the current carrying wire/charged particles is parallel to magnetic field (0 degrees)?

F = 0 N

how to determine the direction of a force experienced by current carrying wire/charged particles in magnetic field?

fleming’s LHR where F is your thumb, B (magnetic field) is your pointer and I is your middle

how to determine the magnitude of a force experienced by a charged particle in magnetic field?

F = qvb sinθ

what to do with direction if charged particle if it has a negative charge e.g electron?

reverse the direction

what is the magnetic field strength outside a solenoid?

MFS will be close to 0 (theoretically assumed)

what is magnetic flux?

measurement of the total magnetic field that passes through a given area; a measure of the number of magnetic field lines passing through a given area

what is magnetic flux density (B)?

strength of magnetic field or number of magnetic field lines per unit area

how to determine magnetic flux?

= BA cosθ in Wb

how to determine magnetic flux density (aka field strength)?

B=magnetic flux/area in Wb

what happens when the plane of the loop is parallel to the field?

0 degrees (cos 90) therefore flux is 0

what happens when the plane of the loop is perpendicular to the field?

cos 0 = 1, therefore flex is at a maximum

what is the law of conservation of energy?

energy cannot be created or destroyed, but only transformed from one form to another or transferred from one object to another

what is electromotive force?

difference in potential that tends to give rise to an electric current; measured in volts (V)

what are some factors effecting voltage (and Faraday’s law)?

• magnetic field strength

• time interval (magnet in and out of coil)

• area (more flux lines)

• angle (perpendicular to area and parallel to field = greater voltage)

• number of turns

any of these factors can change in the formula

why is there a negative symbol in faraday’s law?

indicates the direction of the induced electromotive force (emf) and current resulting from a changing magnetic field, as described by Lenz's law

what happens when an electric conductor has a dynamic interaction with a magnetic field?

EMF is induced

what is Lenz’s law?

states that the direction of induced electric current in a conductor by a changing magnetic field is such that the magnetic field created by the induced current opposes changes in magnetic field that produces it

what is an induced current?

is an electric current generated in a conductor due to a changing magnetic field

what’s the difference between an induced current and a regular current?

An induced current is generated by a changing magnetic field, whereas a regular current flows due to a potential difference consistent over time, without the influence of a magnetic field.

what is the process of lenz’s law when a magnet approaches the solenoid?

• the coil produces a north pole at that end to repel the incoming magnet using RHR

• work has to be done to overcome the repulsion and cause the magnet to continue to move (the mechanical energy required to move it is transformed into electrical energy to conserve overall energy and obey law of conservation)

• a current is induced, which opposes the change in the circuit

• movement causes EMF to be produced

what is the process of lenz’s law when a magnet is stationary to the solenoid?

no voltage recorded, no EMF therefore no current induced

what is the process of lenz’s law when a magnet moves away from the solenoid?

need a south pole set up at top end of solenoid using RHR to attract the receding magnet. This induces a current that opposes the change in magnetic flux (opposite to direction before), creating an opposing magnetic field to minimise the change.

how to determine direction of induced current in a straight conductor?

use fleming’s rule on your right hand

what is Faraday’s law?

states that when the magnetic flux linking a circuit changes, an EMF is induced in the circuit proportional to rate of change of flux linkage

what is the application of faraday’s law?

determine size of induced EMF