Let's talk about Physics.
Moving About
1.1 A typical journey involves speed changes.
1.2 The instantaneous speed is the speed of an object at that particular time. The average speed is the total distance travelled over the time taken.
1.3 Scalar quantities have magnitude only. Vector quantities have magnitude and direction.
1.4 Instantaneous and average speed are scalar quantities. Instantaneous and average velocity are vector quantities.
1.5 Average velocity = change in displacement / change in time
2.1 Velocity of A relative to B = Velocity of A - Velocity of B. Thus from the rule of subtracting velocities, V of A rel to B = V of A + (- V of B)
2.2 Vector diagrams are useful in visualizing the direction, because vector quantities cannot be added linearly like for scalar quantities. Draw a diagram when adding vectors to save your life.
2.3 In order to change the velocity of an object, a net external force is required. Thanks to Newton's first law - an object will remain stationary or moving in a straight line at a constant speed unless an external force acts upon it.
2.4 To change a vehicle's direction - turn the steering wheel. This changes the direction of the driving force. To speed up, hit the accelerator. This increases driving force and the speed of the vehicle. It will accelerate until air resistance and road friction balances it, then it will be constant again (though at a higher speed). To slow down, do not hit the accelerator. The driving force will be zero and air resistance and road friction will gradually decrease until the vehicle comes to a stop. The net force will be backwards as there is no driving force propelling the vehicle forwards (air resistance and road friction acts against the driving force).
2.5 Friction and air resistance act against the direction of the force applied. Too little friction causes things to slide, whereas too much friction prevents things from moving.
2.6 Average acceleration = change in velocity / change in time, therefore a = (v-u) / t.
2.7 Mass is the amount of matter in an object. It is measured in kg. Weight is the force, measured in Newtons (N). It is the force created when a gravitational acceleration acts on a mass.
2.8 Forces acting on a vehicle coasting with no pressure on the accelerator: Air resistance + road friction = driving force, Normal reaction force = Weight force.
Forces acting on a vehicle pressing on the accelerator: Driving force > Air resistance + road friction, Normal reaction force = Weight force.
Forces acting on vehicle pressing the brakes: Driving force going backwards (along with air resistance and road friction), thus net force is backwards. Normal reaction force = Weight force.
Forces acting on a vehicle passing over an icy patch on the road: Too little friction.
Forces acting on a vehicle climbing and descending hills: Weight force still going down. Normal reaction force perpendicular to the road. Other forces parallel.
Forces acting on a vehicle following a curve in the road: Force goes into the centre (centripetal force).
2.9 Newton's Second Law of Motion states that The acceleration of an object depends upon the force acting on the object and the mass of the object. F = ma.
3.1 Kinetic energy is the energy in a moving object. KE = 1/2 mv^2. Work is the force applied to an object over a displacement. Work done on or by an object is equal to the change in energy of that object, thus Work = Change in Kinetic Energy.
3.2 When a vehicle collides with a stationary object or another vehicle, some of its kinetic energy is transferred to the object or vehicle. The remaining energy is either retained by the vehicle or changed into other forms of energy. These energy forms are: Potential energy of deformation, Sound energy, Thermal energy.
3.3 The Law of Conservation of Energy states that energy cannot be created or destroyed, but transformed.
4.1 Momentum is the product of mass and velocity of an object. P = mv
4.2 The impulse of an object is the product of the force applied and the time taken to apply the force. I = Ft. Ft = mv - mu, therefore I = change in Momentum
4.3 The sum of momentum before the interaction must equal the sum of the momentum after the interaction. According to Newton's third law, every action force has an equal opposite reaction force.
The World Communicates
1.2 Waves carry energy.
1.3 Mechanical waves require a medium for propagation, whereas electromagnetic waves do not.
1.4 Medium - not a vacuum
Displacement - How far the wave travels in a straight line
Amplitude - Distance from the equilibrium to the maximum displacement position (crest or trough)
Period - Time taken for 1 wavelength to pass a point
Compression - Region where particles are most compressed in the wave
Rarefaction - Region where particles are most separated in a wave
Crest - Maximum upward displacement
Trough - Maximum downward displacement
Transverse waves - Direction of particle movement is perpendicular to the direction of the energy transfer
Longitudinal waves - Direction of particle movement is parallel to the direction of the energy transfer
Frequency - Number of wavelengths passing a point in a second
Wavelength - Distance from one point on the wave to the next corresponding point on the wave
Velocity - Speed of the wave
1.5 Transverse waves - Direction of particle movement is perpendicular to the direction of the energy transfer
Longitudinal waves - Direction of particle movement is parallel to the direction of the energy transfer
1.6 Velocity = Frequency x Wavelength
2.1 Soundwaves are vibrations of particles in a medium
2.2 Compression - crest. Rarefaction - trough.
2.3 Higher pitch - higher frequency. Lower pitch - lower frequency. Louder - higher amplitude. Softer - lower amplitude.
2.5 Principle of Superposition states that when waves interfere, the total displacement of the medium at any point is the algebraic sum of the individual displacements at that point.
3.1 Electromagnetic waves travel at the speed of light: 3.0 x 10^8 ms^-1 in a vacuum. They do not need a medium.
3.2 Lowest frequency radio waves are reflected off the atmosphere. Other radio and microwaves can reach the earth. Visible light can reach the earth. Infra-red radiation is absorbed. High frequency waves (UV, Gamma, X-rays) are absorbed and scattered.
3.3 Gamma Ray - Geiger counter
X-Ray - Photographic film
UV radiation - silicon chips/detectors
Light - eyes
Infra red - Electronic detectors, skin, thermographic camera
Microwaves - radar device
Radiowaves - Radar device, aerial or satellite dish, antennae
3.4 The intensity of an EM wave decreases as it travels from its source. Inverse Square Law - I is inversely proportional to the distance squared. The energy is spread over a greater area as the distance increases, and the rate of the increasing area is d^2, thus the intensity decreases as the distance increases.
4.1 The Law of Reflection states that the angle of incidence equals the angle of reflection. Reflection from a plane surface will obey this law.
4.2 Telescope - light reflected by a main mirror into a secondary mirror to the eye lens.
Torches and driving lights - Light from filament is reflected on the mirror, then projected.
Satellite dish - Radio waves reflected on the parabolic dish to a receiver at the focus of the dish.
Communiaction - Radio waves reflected off the ionosphere from a transmitter to a receiver.
4.3 Plane surfaces - mirror, Concave - Satellite dish/driving lights, Convex - ??????
4.4 Refraction of light occurs when light "bends" as it travels from one medium into another medium. This bending occurs due to a change in the speed of light.
4.6 Snell's Law states that sin i / sin r = n2 (medium 2) / n1 (medium 1) = v1 / v2
11.58am. Exam in 1 hour 2 minutes.
Time to pack my stuff, get ready and listen to some music. Because that's what I do before exams. No school tomorrow, hell yes. But I'll be studying for Biology and Extension English.
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