Physics Podcast PDF

PHYSICS: GRAVITY:\ All objects with mass produce a gravitational field. The more mass an object has, the greater its gravitational field will be (Earth Gravitational Field Strength is 9.8 Newtons). Weight = Mass \* Gravitational Field strength. Weight is measured in newtons, mass in kilograms and G...

PHYSICS: GRAVITY:\ All objects with mass produce a gravitational field. The more mass an object has, the greater its gravitational field will be (Earth Gravitational Field Strength is 9.8 Newtons). Weight = Mass \* Gravitational Field strength. Weight is measured in newtons, mass in kilograms and Gravitational Field Strength in Newtons per kilogram. RESULTANT FORCES:\ When two or more forces act on an object the resultant force can be found by adding up the individual forces. (If thrust is 50 newtons but drag is 50 newtons the object would be stationary) WORK DONE AND ENERGY TRANSFER: When a force causes a body to move, work is being done on the object by the force. Work is the measure of energy transfer when a force 'F' moves an object through a distance 'd'. So when work is done, energy has been transferred from one energy store to another, and so energy transferred is equal to work done. Energy transferred and work done are both measured in joules. Energy transferred by one of the following four type of energy transfer: mechanical work - a force moving an object through a distance, electrical work - charges moving due to a potential difference, heating - due to temperature difference caused electrically or by chemical reaction and radiation - energy transferred by a wave (such as light, infrared or sound). Doing work is the scientific way of saying that energy has been transferred. DISTANCE AND DISPLACEMENT, SPEED AND VELOCITY: Speed is equal to distance traveled divided by time taken. Speed is measured in metres per second, distance travelled in metres and time taken in seconds. Velocity is equal to displacement divided by time. Velocity is measured in metres per second squared, displacement in metres and time in seconds. FORCES, ACCELERATION AND NEWTON'S LAWS OF MOTION: Newton's second law of motion is resultant force is equal to mass multiplied by acceleration. Resultant force is measured in newtons, mass in kilograms and acceleration in metres per second squared. The equation shows that the acceleration of an object is proportional to the resultant force of the object and inversely proportional to the mass of the object. FORCES AND BRAKING:\ Stopping distance is equal to think distance plus braking distance. Factors that can affect the reaction time include tiredness, drugs, alcohol and distractions. FORCES AND ELASTICITY:\ Change of shape: When a force acts on an object, the object may change shape by bending, stretching or compressing (all three shape changes). A change of shape is called deformation. Elastic deformation is reversed when the force is removed and inelastic deformation is not fully reversed when the force is removed - there is a permanent change in shape Hooke's law: Extensions happen when an object increases in length and compression happens when it decreases in length. The extension of an elastic object, such as a spring, is described by Hooke's law which is force is equal to spring constant multiplied by extension. Force is measured in Newtons, spring constant in Newtons per metre and extension in metres. Energy stored in a spring: Work is done when a spring is extended or compressed. Elastic potential energy is stored in the spring. It can be calculated by using the equation elastic potential energy is equal to spring constant, multiplied by extension squared, multiplied by a half. Elastic potential energy is measured in Joules, spring constant in Newtons per metre and extension in metres. TRANSVERSE AND LONGITUDINAL WAVES: Types of longitudinal waves include sound waves, ultrasound waves and seismic P-waves. In longitudinal waves, vibrations are parallel to the direction of wave travel. They show areas of compression and rarefaction. In longitudinal waves compressions are regions of high pressure due to particles being close and rarefactions are regions of low pressure due to particles being spread further apart. Think of it as a slinky being shaken back and forth, it compresses in some areas. Types of transverse waves include ripples on water, electromagnetic waves and vibrations on guitar strings. In transverse waves, vibrations are at right angles to the direction of wave travel and waves may be thought of as shake or shear waves as the particles move from side to side - crossing the direction of wave travel. Think of it as a rope shaken up and down. PROPERTIES OF WAVES: The rest position of a wave is the undisturbed position of particles or fields when they are not vibrating. The peak is the highest point above the rest position and the trough is the lowest point below the rest position. The amplitude of a wave is the maximum displacement of a point of a wave from its rest position. The wavelength is the distance covered by a full cycle of the wave, usually measured from peak to peak or trough to trough. Displacement is the distance that a certain point in the medium has moved from its rest position. The time period is the time taken for a full cycle of the wave, usually measured from peak to peak or trough to trough and the frequency is the number of waves passing a point. ELECTROMAGNETIC WAVES: There are many different types of electromagnetic waves. There are (starting with the longest wavelength, lowest frequency and lowest energy and ending with the shortest wavelength, the highest frequency and highest energy) radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays and gamma rays. All electromagnetic waves are transverse waves, can travel through a vacuum and can travel at the same speed in a vacuum - 300,000,000 metres per second. Like all waves, electromagnetic waves can transfer energy from one place to another, can be reflected and can be refracted. Each type of electromagnetic wave has a different wavelength and frequency. ELECTROMAGNETISM: When a current flows in a wire, it creates a circular magnetic field around the wire. This magnetic field can deflect the needle of a magnetic compass. A solenoid is a wire coiled up in a spiral shape; when an electric current flows, the shape of the magnetic field is very similar to the field of a bar magnet. The field inside a solenoid is strong and uniform, The small magnetic fields caused by the current in each coil add together to make a stronger overall magnetic field. A solenoid with an iron core is called an electromagnet. The iron core increases the solenoid's magnetic field strength. A simple electromagnet is made by coiling wire around an iron nail. Fleming's left hand rules that the force on a given length of a wire increases when the current in the wire increases and the strength of the magnetic field increases. For any given combination of current and magnetic field strength, the force is greatest when the direction of the current is ninety degrees to the direction of the magnetic field. There is no motor effect force if the current and magnetic field are parallel to each other. Hold your thumb, forefinger and second finger at right angles to each other: the forefinger is lined up with magnetic field lines pointing from north to south, the second finger is lined up with the current pointing from positive to negative and the thumb shows the direction of the motor effect force on the conductor carrying the current. MEASURING WAVES IN A RIPPLE TANK:\ A ripple tank can be used to measure and calculate frequency, wavelength and the speed of waves on the surface of the water. A ripple tank is a transparent shallow tray of water with a light shining down through it onto a white card below in order to clearly see the motion of the ripples created on the water's surface. Ripples can be made by hand but to generate regular ripples it is better to use a motor. First of all, set up the tank with about 5 centimetres depth of water. Next, adjust the height of the wooden rod so that it touches the surface of the water. Now switch on the lamp and motor to adjust until low frequency waves can be clearly observed. Measure the length of a number of waves then divide by the number of waves to record wavelength. Count the number of waves passing a point in ten seconds, then divide by ten to record frequency. Finally, calculate the speed of the waves using the formula, wave speed is equal to frequency multiplied by wavelength.