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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. Measurement of Young modulus of iron

    the unstretched original length (?) of the copper wire. Unstretched original length (?) = ___2.42m_____________________________________ 4. Add 500c.c. of water as load (m) to the water bucker holding with iron wire. Measure the extension of the iron wire (e) from the ruler. 5. Repeat step 4 until the iron wire breaks. Tabulate the results. Mass of load (m) / kg 0 4 6 8 9 10 11 13 13.5 Extension (e) / m 0 0.01 0.012 0.016 0.018 0.02 0.024 0.115 0.143 6. Plot a graph of the extension (e) of the iron wire against the mass of the load (m).

    • Word count: 876
  2. Physics of Rollercoasters

    Tabs were cut into the paper to make it easier to attach it to the rollercoaster. 6. Ramp was stuck between the two pieces of cardboard using tape onto the rollercoaster. The experiment 1. Ball bearing was weighed using electric scales. 2. Height of the rollercoaster at 3 high and 3 low points were measured using string. 3. Total distance of the rollercoaster was measured using string. 4. Ball bearing was dropped from the top of the rollercoaster as a test run.

    • Word count: 1214
  3. Relating the Physics of Rollercoasters to Space Travel

    When the engines are started, the thrust from the rocket unbalances the forces and the rocket travels up until it runs out of fuel, upon which it will fall back to Earth. This change in motion relates to Newton's first law of motion. Similarly, other objects in space also react to various forces. Spacecrafts will travel in a straight line with constant velocity if the forces on it are balanced and only occurs when the spacecraft is a large distance from any large gravity source.

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  4. Practice A2 Investigation: Measuring the torsion of wire

    attachment but hanging freely elsewhere * Attach a torsion bar to the bottom of the wire using a screw * Use a marker as a point from which the period of oscillation can be measured * Pull the torsion bar to any sensible angle, (far enough so the data is accurate but not so far that reaction time becomes a major uncertainty) and release it, allowing it to oscillate freely * Time the period of the oscillations over an accurate, logistically feasible length of time * Repeat this process at least three times for each measurement * Repeat the measurement for wires of same length, different thickness or same thickness, different length A diagram of this experiment is provided below.

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  5. New Technological Advances in Wing Design

    Presently, Boeing and Airbus are designing the winglets so that the cant angle is able to change during flight. It will be altered for take-off, climb, cruise and landing approach. This way, drag will be a minimum, and the fuel efficiency will be constantly at 5%. Also, because there will be less fuel needed to fuel the engine, the engine will make less noise, meaning the landing will be quieter. The winglets will also be able to be flattened, which will create a greater lift force on the plane. Boeing has patented the winglet design, which involves using smart alloys (or shape-memory alloys)

    • Word count: 1043
  6. Lift

    The higher the L/D ratio, the higher the efficiency of the aircraft. The angle at which the front of the wing is inclined affects the amount of lift produced, as well. The 'angle of attack' is directly proportional to lift. This is because the surface area hitting the air is greater, meaning more air molecules act to create a force, which means that lift is greater. Nevertheless, this only works up to an angle of about ~10o. If the angle gets too high, then air molecules start sticking to the wing, which means that there is no constant flow of fluid, which is essential for lift.

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  8. Modeling a basketball shoot in the lab

    Putting t into equation (6), the equation of trajectory is, y= x tan ? - g/2u2 cos2 ? This shows that the object can be described as a parabolic path since it is comparable with the equation y= - kx2 + c. Theory- PROJECTILE MOTION AT AN ANGLE A general case of projectile motion occurs when the projectile is fired at an angle. y=0; 1. Upward direction is positive. Acceleration due to gravity (g) is downward thus g = - 9.8 m/s2 2. Resolve the initial velocity vo into its x and y components: vox = vo cos ?

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  9. Physics of scuba diving

    (this is also why it is important for submarines to be quiet to avoid detection). I have chosen to focus on the effects of the changes in pressure experienced by divers, as I feel this is the most important aspect of physics that needs to be appreciated for safe Scuba diving. A brief history of diving The first recorded incidence of diving comes from ancient Greece (1), divers jumped into the water carrying a 15kg stone, sank to around 30 metres and cut the sponges away from the sea bed.

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  10. Measuring The Constant g; The Acceleration Due To Gravity

    After measuring the time of 20 back and forth swings, I divided by that number to get the average duration of a single period. Then by that above formula I calculated g, to a high level of accuracy, having rearranged it to this form: g = 4?(L/P( Ultimately, I calculated it to be g ? 9.81 ms-2 with a percentage uncertainty of just ?1.3%. Introduction In this investigation I am going to be obtaining a measurement for the gravitational constant of acceleration 'g' using two main methods, in order to compare their accuracy, and hence determine the more precise value.

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  11. Centripetal motion experiment. Objective To study the relationship between the angular speed and the centripetal force and verify the expression of centripetal force.

    * Use nylon spread, which is inextensible to lower the error. Theory To keep the body moving in a circle, the centripetal force is required. It is provided by the external resultant force towards the centre. To keep the radius unchange, the cantripetal force should alter the angular speed of the object. However, it does no work on the body and the kinetic energy of the body remains unchanged. By comparing the horizontal and vertical component of the tension, the expression of tthe centripetal force can be deduced. We can find out that the centripetal force=Tsin?=m?(lsin?), so T=ml?2.

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  12. Quality of Measurement - Physics AS

    The equation I'm going to use to plot as the x-axis against the distance fallen will be (S = ut + 1/2 at�) which will relate to: (y = mx + c) where ut = c so that can be excluded as ut = 0 and mx = 1/2at� therefore x = 1/2t� and m = a so the x-axis will be plotted to 1/2t� where t is the time I predict that there will be a constant gradient of around 9.81ms-� between the height being dropped and 1/2t� helping me prove "g" by freefall.

    • Word count: 1431
  13. Scalars and Vectors

    Ice shut airport runways, roads were gridlocked and trains broke down. If the average, young or middle-aged citizen finds it difficult to survive in conditions like this, imagine how the elderly must find the conditions of this year's winter. This brings me to talk about how elderly people must suffer from the freezing cold in their homes, vulnerable to many kinds of hazards, right from their front door step. Icy conditions have led to hundreds, even thousands more hospital admissions this year in the United Kingdom - most of these admissions have been elderly people.

    • Word count: 994
  14. Determining the force constant

    Also, we assumed that the effect of air resistance acting on the mass and the spring is negligible . Difficulties encountered When conducting the experiment, we initially used a spring which cannot be extended significantly. As a result, we cannot conduct the experiment efficiently as we couldn't see the tiny change in period.

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  15. Gravity and Acceleration

    1993-2002 Microsoft Corporation. All rights reserved. The acceleration of a freely falling body is equal for all masses but due to air resistance it varies. In this experiment the acceleration of falling bodies are calculated and compared using two different set -ups. Apparatus: 1. Ticker Tape 2. Retort stand 3. Pulley 4. String 5. Weight 6. Photogate 7. Lab Pro Interface 8. Picket Fence 9. Trolley 10. Laptop/computer Method: Using the Photogate: 1. The lab pro interface is connected to the photogate and the laptop.

    • Word count: 1168
  16. Force of friction

    And the value of is roughly proportional to the normal force R. where is the coefficient of static friction at maximum at the contact surface. Kinetic friction : However, the friction acting on a resting block is less than until the block starts to move. For example, once the body starts to move over the rough surface, the friction would decrease slightly to a value known as kinetic friction . So is slightly less than but it is still approximately proportional to R. where is the coefficient of kinetic friction at the contact surface.

    • Word count: 1635
  17. Measuring Young modulus of copper

    The wire is loaded in steps and be recorded the extension e produced. Data Analysis and Results 1. Measurements of the diameter of wire 1st measurement 2nd measurement 3rd measurement Diameter d/m 0.0003 0.0003 0.0003 Mean diameter of wire d = 0.0003m 2. Measurements of the original length of wire 1st measurement 2nd measurement 3rd measurement Length l/m 2.9960 2.6400 3.7730 3. Measurements of the extension of the wire with load and hanger(0.0996kg) Load m/+0.0996kg Extension e/m 1st measurement 2nd measurement 3rd measurement 0.0000 Failure 0.0000 0.0000 0.1000 Failure 0.0010 0.0015 0.2000 Failure 0.0020 0.0020 0.3000 Failure 0.0025 0.0030

    • Word count: 921
  18. charging a capacitor at a constant rate(C08)

    Set the CRO to d.c. and the sensitivity to 1V/cm. 2. Set the time base to any high value so that a steady horizontal trace is displayed. Shift the trace to the bottom of the screen. 3. Short out the capacitor by connecting a lead across it and adjust the 100k? potentiometer for a suitable current, 80�A. 4. Remove the shorting lead and the capacitor will charge up. Note what happens to the microammeter reading and the CRO trace.

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  19. In this experiment, we investigated the relationship between the difference in work and mechanical advantage. Furthermore, we wanted to determine the difference between total work done lifting a 1kg mass up a height

    How much easier and faster a machine makes your work is the mechanical advantage of that machine. In our experiment, mechanical advantage can be measured by the equation: length of the ramp / the height of the ramp which we're going to use to find the difference of work between taking the 1kg mass up and dragging it up the ramp. We are first going to set up the ramp with a height of 5 books, then measure the length of the ramp which is about 1 meter.

    • Word count: 1532
  20. Callibrate a Hall Probe: Planning

    n = no. of electrons per unit volume (e/m3) e = electron charge (1.6 x 10-19 C) d = thickness of film in Hall probe (m) Formula 2 Diagram of Apparatus for calibration Draw diagram here Method of calibration 1. Place the Hall probe in an area with no magnets and zero it. 2. Set up Helmholtz coils as above. The current going through each coil should be 0.5A. 3. Use a wooden ruler, held by wooden clamps, positioned behind and beside the coils to find the centre of the magnetic field. 4. Position the Hall probe in the centre so that it is perpendicular to the direction of the field.

    • Word count: 928
  21. Building a hovercraft with household objects.

    * Razor knife * Staple gun * Duct tape * Spray Adhesive * Silicon Caulking * Marker * 2 Foot string * Hammer * Extension Cords * Stool * Measuring tape * Wrench * Ratchet * Drill Procedure 1. Tie a permanent marker to the end of a 2' long string, with a loop at the opposite end of the string. 2. Measure the exact center of the board, and drive a nail into it. 3. Loop the end of the string opposite of the marker around the nail.

    • Word count: 2556
  22. Free essay

    Investigating the Damping of Motion in a Simple Pendulum through Induced Eddy Currents

    I will start recording, and then release the pendulum. Using frame by frame analysis of the video I will determine the frame when the pendulum was released, and the first swing in which the pendulum achieves strictly less than 15 degrees of deflection. By working out the number of frames this takes, and dividing by the frame rate of the camera, I can calculate the time taken. The equipment will be set up as in the diagram on the next page, although the camera is not shown in the diagram.

    • Word count: 946

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