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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.

  • Marked by Teachers essays 1
  • Peer Reviewed essays 9
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  1. Marked by a teacher

    Experiment to determine gravity from a spring using digital techniques

    3 star(s)

    Procedure Apparatus * Stand * Motion sensor * Computer with datastudio installed * Slotted masses and mass holder * CD * Pointer * Half metre stick * Balance accurate to 1g * Lab jack * Spring Part One * The experiment is set up as shown. * Datastudio is opened on the computer, and "create experiment" is clicked. * In the "create experiment" window, the motion sensor is selected. * In the measurement window, "Position, Ch1 & 2 (m)" is selected. * In the "display" window, the "graph" selection was double clicked to set up a graph of the results.

    • Word count: 1561
  2. Peer reviewed

    The Compound Pendulum

    5 star(s)

    * 'h' is the distance of the pivot from the centre of gravity in metres - independent variable * 'g' is the acceleration due to gravity - dependant variable By plotting T against h at this point, the graph will be a parabola. This is because T is proportional to h, and the equation is not in the form of y = mx + c, in which case the graph would be a straight line. The above equation can also be written including the mass of the pendulum.

    • Word count: 1972
  3. Viscosity Experiment. The aim of my investigation will be to analyse the relationship between several variables, which are defined by stokes law, and conclusively to apply these in order, to calculate the viscosity of the fluid from my results.

    surface or "redwood viscometer", which involves the liquid to flow through a narrow tube driven by its own head of pressure, but due to the lack of apparatus, I chose to do the falling ball viscometer, as this experiment gave an absolute measurement of viscosity, and was too, the most feasible method to be performed in a lab. I will be unable to calculate the viscosity using the above equation, because "F" will not be able, to be measured directly with the method I will be using.

    • Word count: 1559
  4. Experiment to calculate spring constant of 2 springs

    The mass of the cart is recorded, and extra mass bars are added to it, in order for the cart to have differing periods depending on what mass is on it. The theoretical period for each of these masses is calculated and compared to the period calculated experimentally. Procedure Apparatus * Trolley * Two springs * Force sensor * Dynamics track * Photo gate * Mass bars * Five pattern picket fence * Computer with datastudio software * Interface Part 1 * The interface was connected to the computer, and the data studio document P15 Prelab Oscillation.DS was opened up.

    • Word count: 1452
  5. How can I work out the Young's Modulus of copper wire?

    Once again, numerous measurements could be taken to give a more reliable result. Breaking of loop The loop breaking has a massive detrimental effect on the experiment, completely voiding its accuracy. Thickness of wire (�1.8%) Taking more readings at further points down the wire and then finding an average will give a more certain result for this. The micrometer must also be calibrated. Values of extension between 10N increments Using 5N weights instead of the 10N ones should make this experiment more precise, as more values will be used to determine the average, making my result more accurate.

    • Word count: 1275
  6. Experiment test for F = m2L by whirling a rubber bung (centripetal force)

    Centripetal force = T sin ? Centripetal force = m?2r T sin ? = m?2r T sin ? = m?2L sin ? ? T = m?2L The vertical component of the tension balances the weight of the rubber bung. T cos ? = W The nylon string is passed though a glass tube to prevent external force acting on the system by the hand. During the experiment, the paper marker was kept in a constant position below the bottom of the glass tube to help us to keep the angular velocity of the rubber bung constant.

    • Word count: 1423
  7. What are the physical quantities that affect the value of centripetal force when a body in circular motion? What is the force exerted on the object when the object is doing a horizontal circular motion?

    The experimental centripetal force (Fc) of the rubber stopper swinging around is calculated by using: Equation 2 where ms is the mass of the rubber stopper, and the other variables as before. Centripetal means "center seeking". There are two main forces at work in this laboratory exercise. "Opposing" the centripetal force is the theoretical, accepted force due to the weight of the screw nuts pulling the string down through the bottom of the hollow glass tube: Equation 3 where g = 9.8 m/s2, the accel.

    • Word count: 1011
  8. Young Modulus of Copper

    Afterwards , they try to explain this with the atomic model and here below is the common behavior of some pure metals : As for this experiment , we are trying to verify the above results and find the Young modulus of copper , which is its stiffness . And this is going to be done with the following set-up : For the sake of a more accurate measurement , this experiment will be separated into two parts . In the first part , we will add the slotted mass to the load gradually until the copper wire breaks ,

    • Word count: 1351
  9. A careful quantitative study of the relationship between the velocity of a trolley down a slope and the angle of the slope.

    Experiment Equipment: * one pair of light gates * computer to collect light gate data * ruler * piece of wood or other smooth material for slope, about 80cm long * stack of books * trolley * piece of card, 10cm long * blu tack or other adhesive to attach the card to the trolley Method 1. The piece of wood was positioned to rest at one end on the table, point C, and the other end on the stack of books, point E.

    • Word count: 1446
  10. Measuring g in more than one way

    Results: Mask Size (cm) 8 10 Drop # Acceleration (m s-2) 1 9.63 9.68 2 9.48 9.97 3 10.03 10.02 4 9.67 9.88 5 9.69 9.75 6 9.78 9.61 7 9.44 9.63 8 9.73 10.1 9 9.8 9.79 10 10.03 10.08 11 9.54 9.84 12 9.66 9.67 13 9.99 10.04 14 9.74 9.79 15 9.72 9.68 Average(m s-2) 9.728666667 9.83533 This is the table of results for the experiment. It is clear that the results are fairly accurate for the value of 9.8 m s-2 for g. The result for the greater mask size is most likely more accurate as any deviation from the expected mask size due to the angle it's dropped at will have less effect over a greater mask size.

    • Word count: 1351
  11. 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
  12. 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.

    • Word count: 1113
  13. 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
  14. 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
  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. 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.

    • Word count: 1246
  18. 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
  19. Free essay

    Space Elevator

    The current problems space scientists encounter with traditional launching pad are: � The huge energy consumption needed to launch a spatial object � The weight constraints that it generates � The associated risks (fire, rocket destabilization) Thus the main advantages that a space elevator could allow are - � The weight is not a problem anymore, therefore the number of payloads onboard is no longer restricted � Launches are definitely cheaper All of this could call into question the current advanced technologies because of the weight and price constraints that would be partly removed.

    • Word count: 1541
  20. Testing an LDR

    When cadmium sulphide (CdS) is subjected to light, the absorption of photons excites electrons to a higher energy state. When in this higher energy state, the electrons are able to flow as a current. The more electrons absorbed by the CdS, the more charge carriers available, and thus the less resistant it becomes Alternative methods I discovered through my research for detecting light levels include photovoltaic cells1, which convert photons into electricity. However, it would not be as easy to adjust the sensitivity or range as in an LDR, which can be placed in a potential divider circuit.

    • Word count: 1759
  21. Determinating of acceleration due to gravity by timing a simple pendulum

    Change the value of d (the distance of the bob from the ground) stepwise using a step size of about 5cm. Repeat steps 1 to 3 for a total of 10 different lengths. Precaution * Start the stop watch and on the count of zero and stop it on the count of 20. Explanation:When we loosen the hand which holds the bob through an angle about 200 , the bob starts to oscillate, as it hasn't swing forward and back for once, so we should count it for the number" zero".

    • Word count: 1157
  22. Investigation of determination of flux density of magnets(plane)

    These can be represented by holding the thumb and first two fingers of your left hand so that they are mutually at right angles. Fingers represent: Thumb shows the direction of the movement ( the force ) The first finger shows the direction of the field The second finger shows the direction of the current The production of this force is known as the motor effect, because this force is used in electric motors. I a simple motor, a current flowing in a coil produce a magnetic field; this field interacts with a second field produced by a permanent magnet.

    • Word count: 1230
  23. movement in sports

    Below is the formula of the MA and VR: Velocity Ratio = Distance to the Load Mechanical Advantage = _Load_ Distance to Effort Effort Diagram List of Apparatus * Bores * Clamp stand * String * Clipped roller * Masses ranging in weight such as 10g, 20g 50g and 100g * Ruler with hooked nails put into every 5cm Preliminary Work I carried out some preliminary work before the experiment on the basis that it would help me decide the weight I would use.

    • Word count: 1466
  24. Design of Customer Input Form

    In this code, an "L" represents a letter and a "9" represents a number. So for a postcode, the code would read "LL00 9LL"; two letters, up to two numbers, one number then two letters to finish. Length Check This limits the number of characters that can be typed into a field. It is most useful for a field with a specific number of characters like telephone number. A telephone number always contains the same number of characters, so this facility allows you to ensure that no extra numbers are accidentally typed in. It can also be used for other fields without a specific number of characters.

    • Word count: 1871

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