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AS and A Level: Fields & Forces

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What are gravitational fields?

  1. 1 A gravitational field is a region where a mass experiences a force. The field strength, g, at any point in the field is given by g=F/m and the value of g on the Earth’s surface is taken to be 9.81Nkg-1.
  2. 2 Field lines point towards the centre of the Earth and are radial. Over small distances, near Earth's surface, g can be considered constant so field lines are parallel and the field is uniform.
  3. 3 G was calculated by Henry Cavendish by measuring the force of attraction between two lead spheres of known mass and separation. The force between two masses is given by F = Gm1m2/r2 and this is called Newton’s law of universal gravitation.
  4. 4 Inside the Earth, g falls from 9.81 to 0 Nkg-1 so we cannot use the inverse square law for r < RE.
  5. 5 Combining Newton’s law with circular motion can be used to calculate distance to geostationary satellites.

What are electric fields?

  1. 1 An electric field is a region where a charge experiences a force. The field strength E at any point in the field is given by E = F/Q. The force between two charges is given by Coulomb’s law.
  2. 2 For radial fields, E = 1/ Q/r2 and this is another inverse square law. For uniform fields, E = V/d.
  3. 3 Uniform electric fields can be set up to accelerate charges. The work done accelerating a charge through a p.d. V is given by W = QV. The unit of energy can be given in Joules (J) or electronvolts(eV).
  4. 4 When a charge enters a uniform electric field, such as between the deflection plates of an oscilloscope, there will constant acceleration and so suvat equations can be used.
  5. 5 For all electric fields, equipotential lines are drawn perpendicular to field lines. For radial fields, always show at least 3 equipotential lines as concentric circles with increased spacing.

    The equipotential lines can be experimentally determined using conductive paper, metal electodes and a voltmeter to map out points of equal potential. You should be able to draw equipotential patterns for two point charges.

Similarities and differences between gravitational and electric fields.

  1. 1 Gravitational forces are always attractive but electric forces can be both attractive and repulsive. There are no negative masses but there are negative charges.
  2. 2 The ratio of the strength of the two forces is huge. For two electrons, FE/FG is approximately 1042. This demonstrates how much stronger the electric force is compared to the gravitational force over the same distance.
  3. 3 Both fields obey an inverse square law.
  4. 4 Over short ranges, electric forces dominate but over much larger distances, say between planets and their moons, gravitational forces dominate because the attractive and repulsive electric forces tend to cancel out.

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  1. Investigation to find out what affects the size of a shadow.

    Hypothesis I predict that the closer the object is to the light source the larger the shadow will be. Therefore the further away the objects from the light source mean the shadow will be smaller. This is due to many factors regarding how light travels and the distance to object lies from the source light. We know that light travels in straight lines so when an object is place in front of a light the light cannot travel around the object or through it so the object blocks out the light. This means that if the objects are closer to light the light source the more light is blocked out.

    • Word count: 1194
  2. Electromagnet Investigation

    When the domains are pointing in one direction a magnet is made. The strength magnetic field produced by the solenoid is then increased greatly. The higher the current passing through the coil the stronger the magnetic field this is because there will be more electrons (e ) moving there will be. Without being placed in magnetic field. With being placed in a magnetic field. (Solenoid coil) If the double the amount of turns we will get double the amount of electrons moving in that location or area, increasing the magnetic field because of smaller individual magnetic field will merge making a tug of war effect.

    • Word count: 1856
  3. Hockey Skills

    The field players can be put into three general categories - attackers, defenders and midfielders. While no player (other than the goalkeeper) has an exclusively defined role, the attackers are generally on attack, the defenders are generally on defence, and the midfielders do a bit of both! Stick handling An essential skill necessary for playing hockey is the ability to control, pass, push, stop and shoot the ball with your hockey stick. This is known as stick work, or stick handling. It is both beautiful and impressive to watch a player with good stick handling skills control the ball while sprinting the length of the field, or weave through the sticks and legs of defenders to create an open shot.

    • Word count: 1091
  4. Investigating the Mechanics of the 100 Metre Sprint

    Initially the athlete should concentrate totally on his starting technique, which he has fine-tuned in training. Irrespective of the lane or adversaries, he now focuses on a smooth acceleration towards attaining his maximum speed. Once he has attained his top speed, he now relaxes totally in order to maintain his speed with the least amount of unnecessary interaction from muscles or parts of the body not being used for sprinting. The finish also requires some though because a centimetre gained by a correct finishing technique can win a race, a positive and active forward lean can help to achieve that.

    • Word count: 1674
  5. Charge To Mass Ratio For An Electron

    Comparing this experimental value to the theoretical value which is 1.76�1011 coulombs/kg makes a 7.38% experimental error. One of the reasons that this error can occur is related to earth's magnetic field and causing force on the electrons. In conclusion a charged particle will experience a force when moving through a magnetic field and also as the radius of the coil increases as electron flow the magnetic filed decrease. This can also prove that these two are inversely proportional. Introduction In 1897 J.J. Thomson made the first measurements of the charge to mass ratio of an electron (e/m), using cathode ray tub.

    • Word count: 2294
  6. Simulating Asteroid Impact

    for objects moving towards the Earth. In other words a falling object has a negative displacement. For objects moving away from the Earth, d will be positive (+). Notice that time, t, is still a part of equation (2). By substitution, we can eliminate t and can then calculate vf based solely on the distance the object falls. The initial velocity in these experiments is equal to zero, since the ball bearing is not moving prior to being released. This then simplifies the equations (1) and (2) to: (3) vf = -gt (4) d = -0.5gt2 By manipulation of equation (3)

    • Word count: 1522
  7. The Physics of Curling

    to guide the stones from a fixed distance and as proximal as possible to a center target. Furthermore, there are two sweepers that attempt to guide the stone as close as possible to the center target(similar to a target one would see at an archery range except this target is embedded into the ice) --- the game requires an immense amount of strategy and hitting the stone (which is essentially the puck) at tactical angles while taking into consideration physical forces which is where the beauty of physics comes into this sport as it does with essentially almost every aspect of nature.

    • Word count: 714
  8. An Experiment to Evaluate the Acceleration due to Gravity using a Spiral Spring

    8.28 8.33 8.53 8.32 0.11675 8.336 0.174 1.0 9.25 9.26 9.19 9.12 9.28 0.06519 9.22 0.213 1.2 9.95 10.19 9.88 10.03 10.29 0.16947 10.068 0.253 Figure 3 Figure 4 Load On Spring (kg) g (ms-2) 0.2 2.73 0.4 5.69 0.6 7.58 0.8 7.73 1.0 8.18 1.2 8.34 The mean value for g is calculated as 6.71 ms-2 with the standard deviation calculated as 2.17 Calculations Calculating the extension of the spring or b b=(l-l0) b is the extension on the spring when a mass is loaded, l is the total length of the spring with the mass attached and l0

    • Word count: 1068
  9. The physics of riding a bicycle entails many different properties.

    A bicycle was at one point the epitome of modern moving conveyance. The invention of the wheel allowed this. Previously, everyone had to walk everywhere they had to go. In the rain, sleet and snow, walking was the main mode of getting from ?here? to ?there?. The bicycle has taken different forms. There have been tricycles, a bike with three wheels, and a unicycle, which was used in circuses that had a rider on one wheel. When I first learned how to ride a bike, I fell a lot.

    • Word count: 1243
  10. Use the following terms correctly in describing the forces and elements of a roller coaster.

    There are actually two specific types of energy involved: potential and kinetic. A roller coaster cart has a large quantity of potential energy at the top of a hill. Potential energy, which is stored energy that depends on the mass and height of the object, is high at the top of the hill because the cart is very high off the ground. As the cart descends down the drop, it loses potential energy in accordance with height. However, the cart subsequently gains kinetic energy, which is the energy of motion that depends on the mass and speed of the object.

    • Word count: 925

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