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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. 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
  2. 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
  3. Power Lab Report

    I made a table with columns name, Fg(N), Vertical Height (m), Work done, Power, Ranking 2. We measured the height of a one step, and then multiplied it to 14 since the stairs has 14 steps. 3. Then I used the stopwatch to measure how fast Xerxes made it to the top. Then record it on the time column of the table. Then Xerxes timed how long I took to reach the top. 4. Then other partners did just like what we did, they timed each other. 5. After that, we share the data we got.

    • Word count: 645
  4. Simple Harmonic Motion

    Put a cross one the tape at the position just beneath the pin of the ticker-timer to indicate the equilibrium position of the mass. 6. Pull the mass towards the ticker-timer through different distance. 7. Switch on the timer and at the same time release the mass. Stop the timer when the mass reaches the opposite side. Question Answering: 8a) A motion which said to be S.H.M. if the acceleration of the motion is always directed toward a fixed point and the magnitudes of the acceleration is directly proportional to the displacement to the fixed point.

    • Word count: 919
  5. 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
  6. As Fast As you can

    Thinking Distance Thinking distance is calculated by the general equation: Thinking distance is the distance covered in the time it takes for a reaction to occur. In what can be a fraction of a second, a substantial amount of ground can be covered. Human reaction time is usually between 0.2 and 1 second. However, there can be various conditions and factors that can dramatically affect this. Smoking whilst driving or in general causes a stimulus affect which can speed up reaction times or create a neurotic result.

    • Word count: 957
  7. Does the mass of a block of wood effect the size of a frictional force?

    Extra mass placed on block (g) Total Mass (g) Force exerted on block on the smooth surface (N) Force exerted on block on the wooden surface (N) Force exerted on block on the rough surface (N) 105 50 155 0 0.1 0.2 105 100 205 0.1 0.3 0.4 Prediction I predict that the mass of the block will have an effect on the amount of frictional force. My preliminary experiment results prove this as when we put more weight on the block the frictional force became greater. When the block is pushed down onto the surface of the floor, this causes the two surfaces to lock.

    • Word count: 929
  8. Elastictvy of Copper investigation

    I think that the copper wire will have a young's modulus of about 130 Gpa(GigaPascals / Kn/mm), as the secondary source has worked this out The stretching force which extends material by equal steps is called Hooke's law. Hooke's law states that the force needed to stretch a spring is proportional to the extension of the spring from its natural length. The formula used for Hooke's law is Force, F=Ke. The K is the spring constant (measure in force by length)

    • Word count: 2750
  9. Investigate how the static force exerted on the front axle varies with the vertical load applied to the rear end

    A hook represents the towing mechanism of the recovery truck. Diagram of apparatus: The rear axle consists of a metal bar, placed through the drilled hole R, which is suspended from an elastic band on either side of the wooden block. The elastic bands hang of another metal bar which is held horizontally by a clamp stand. The front axle consists of a metal bar, placed through the drilled hole F, which is balanced on small wooden blocks placed on either side of the wooden block.

    • Word count: 751
  10. Electromagnetic Induction

    If an electric effect can produce a magnetic effect, maybe the reverse may also be true, i.e. a magnetic effect may produce an electric current. APPARATUS * Ballistic galvanometer * Horseshoe magnet * Bar magnets * Leads * Wired metal rod * Induction coils * 60 microamp galvanometer METHOD 1. The coil was connected to a Microammeter. The N pole of the magnet was inserted into the solenoid and a description was recorded.

    • Word count: 338
  11. 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
  12. Physics Spring Coursework

    To do this different arrangements of springs (each with spring constant k) were used to form spring systems of different spring constants. To work out the spring constant of each arrangements, ktot-1=k1-1+k2-1 (for springs in parallel) and ktot=k1+k2 (for springs in series) were used. The laws of logs can be used to change the formula lnT= ln(pkqmr ) into a straight line graph, in the form y=mx+c. Using Law 1, ln(pkqmr) = lnCHNKWKS -�"TEXTTEXTVZFDPPFDPP^FDPPFDPP`FDPPFDPPbFDPPFDPPdFDPPFDPPfFDPPFDPPhFDPCFDPCjFDPCFDPClFDPCFDPCnFDPCFDPCpFDPCFDPCrFDPCFDPCtFDPCFDPCvFDPC FDPCxFDPCFDPCzFDPC FDPC|FDPC FDPC~STSHSTSH�h B This expIntroduction The aim of this experiment was to find out if the time period of a vertical mass oscillating system is dependant on the spring constant (k)

  13. 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
  14. Sliding & Friction Lab Report

    Your car can move faster because less force is needed for the car to move. On the hand, when you are driving on a gravel road, you need greater force to cause motion because the surface is not smooth as asphalt paved road, which is flat. There are three different types of variables in this experiment. The independent variables in this experiment are the surface area, the block material, the sliding surface, and the mass of the block. The controlled variables in the experiment are the sliding surface, the block mass, and the surface area.

    • Word count: 939
  15. Investigation to determine the viscosity of glycerol.

    Viscosity is basically the resistance between the particles within a fluid. In a solid molecules are tightly packed i.e. there is a strong intermolecular force. Therefore when you move a solid, it moves as a whole as all the particles move together. In a fluid this is not the case. This is because due to lower intermolecular force the particles move at different velocities in relation to each other. This feature can be understood by discussing what happens when pouring a jug of water into a glass. In liquids the molecules flow in layers.

    • Word count: 9042
  16. The experiment involves the determination, of the effective mass of a spring (ms) and the spring constant (k).

    These measurements were then noted in a copy of the following table: Mass/Kg x number of oscillation's Time for 'x' oscillations (in seconds) xT av/s T/s T2/s2 ?xT/s % unc in xT % unc in T2 ?T2/s2 0.100 0.200 0.250 0.300 0.400 0.450 0.500 0.600 xT xT xT The quantities could then be derived in the following ways. To find the quantities first it was necessary to draw a graph of the results taken and to get the graph to be a straight line graph and so as to be of use the equation of T2 had to be rearranged as shown below: T= 2??(m+ms)

    • Word count: 2161
  17. Investigating the relationship of projectile range and projectile motion using a ski jump.

    Hypothesis I predict that the higher ramp, the higher the velocity therefore an increase in range. Null Hypothesis There will be no relationship found between the height of the ramp, velocity and the range of the projectile. Rationale The displacement, velocity and acceleration of the projectile are all vectors. The forces of the projectile motion can be treated separately, so they can be resolved into horizontal and vertical components. They are independent of each other; that is, neither motion affects the other. We can label these components x and y. The horizontal component can be represented as Vx and the vertical component as Vy.

    • Word count: 2457
  18. What Affects the Strength of Magnetism Exerted By an Electromagnet?

    The Earth has a magnetic field. There are also poles named 'Geographically' North Pole and South Pole. The North Side of the compass needle will naturally point to the geographic North Pole. However, this would prove whole theory of magnetism incorrect. We have therefore decided that Magnetic South is Geographic North. Thus, the North Pole of a compass needle points 'Geographic North' and 'Magnetic South'. There are certain 'Rules of Magnetism' which have been founded. One of the most important is that: Lines of force will never cross. This becomes evident when we sprinkle 'Iron Filings' around a magnet.

    • Word count: 4203
  19. Rules and Laws in Football

    The area bounded by these lines and the goal line is the goal area. The Penalty Area A penalty area is defined at each end of the field as follows: Two lines are drawn at right angles to the goal line, 16.5 m (18 yds) from the inside of each goalpost. These lines extend into the field of play for a distance of 16.5 m (18 yds) and are joined by a line drawn parallel with the goal line. The area bounded by these lines and the goal line is the penalty area. Within each penalty area a penalty mark is made 11 m (12 yds)

    • Word count: 3095
  20. To calibrate an uncalibrated Hall probe and use it to investigate how the magnetic flux density mid-way between opposite poles of two permanent bar magnets varies with the separation of the bar magnets.

    The potential difference created is known as the Hall effect ii. Now, at certain currents, values for both magnetic flux density and the Hall voltage can be measured. A graph of magnetic flux density can be plotted against the Hall voltage. This should create a straight line through the origin. This is because the magnetic flux density is directly proportional to the Hall voltage. The forces acting on the charge carriers in the Hall probe can show this. The electrons initially experience a magnetic force due to the magnetic field created by the solenoid.

    • Word count: 904
  21. Slowly trudging through the swampy field silhouetted by the moon, was the fifth victim of the Buttermilk Bluebeard

    It was violating this rule that got Andy killed. It started as soon as he climbed out of his bedroom window at 10:30PM. He shuffled down the cast iron drainpipe down the side of his house to the ground, he sneaked around the house in total stealth making sure nobody saw him. He crossed the well-lit main road, which spoiled the serenity of the village, bringing more people to the village who bought houses for obscene amounts of money and the Buttermilk Bluebeard.

    • Word count: 638
  22. Aims: 1. To record changes in species composition from a grassland to a woodland.2. To record changes in height of the ground at metre intervals

    In the wood there will be more variation and less dominant species, therefore, the rate of succession in the wood will be more obvious than on the field because of less human interference. Apparatus: * 0.5 x 0.5m quadrat frame * 2 canes * 1m rule * Spirit level * Tape measure * Light string * Toilet roll tubes * Identification keys Method: I will find a area

    • Word count: 412
  23. Describe two research studies into animal navigation.

    It was also found that young pigeons had difficulties in both sunny and overcast environments, suggesting that using the earth's magnetic field to navigate is innate, whereas using the sun comes with experience. Mouritsen and Frost looked at Monarch butterflies and the way in which they navigate. They condicted an experiment whereby butterflies were tethered in a specially built flight simulator that simulated flying with the use of airflow from below the butterflies. This, however, did not affect the direction in which the butterflies headed.

    • Word count: 806
  24. Physics Coursework, Visit to Holly House

    Only the part of the body that is to be scanned is scanned, and the patient can either enter head first or feet first, which is determined by the type of radiographic exam to be performed. Once the area of the body that is to be examined is in the exact centre of the magnetic field of the scanner then the examination may begin. The Examination Prior to allowing a patient to enter the scan room, he or she is thoroughly screened for metal objects.

    • Word count: 2348
  25. 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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