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GCSE: Forces and Motion

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Balanced and unbalanced forces

  1. 1 There are many words which mean force. E.g. push, pull, friction, weight, air resistance, tension, thrust. All are measured in newtons (N).
  2. 2 When a body is acted on by more than one force at the same time, the overall force is called the resultant force. E.g. if a car is pushed to the right with a force of 500 N and to the left with a force of 200 N, the resultant force is 300 N.
  3. 3 When the resultant force is greater than zero, the forces are unbalanced and this will cause a change in speed or direction, or both. For the example of the car, the 200 N resultant force would cause the car’s speed to increase so the car is accelerating.
  4. 4 What if the brakes are applied to the car? The braking force acts in the opposite way to the direction in which the car is moving. This time the speed decreases and the car is decelerating.
  5. 5 When the resultant force is zero, the forces are balanced. The body will continue to move with a constant speed in the same direction. This is true for a skydiver falling with a constant speed called the terminal speed. The air resistance is equal to the weight.


  1. 1 When the forces on a body are unbalanced, the resultant force, F causes an acceleration, a. We can calculate the acceleration using an equation F = ma.
  2. 2 In this equation m is the mass of the body measured in kilograms (kg). F is the force measured in newtons (N) and a is the acceleration measured in m/s2.
  3. 3 You should practice how to write the equation in three different ways by rearranging it:

    1) F = ma
    2) m = F/a
    3) a = F/m
  4. 4 Suppose a resultant force of 20 N acts on a body giving it an acceleration of 4 m/s2. What is the mass of the body? Choose an equation for m, so we use m=F/a = 20/4 = 5N.
  5. 5 A car of mass 2000 kg is acted on by a force of 500 N. What is the acceleration? Choose the equation for a, so we use a = F/m = 500/2000 = 0.25 m/s2.

Motion under gravity

  1. 1 The weight of a body, W is a force and it can be calculated from the equation W=mg. g is the gravitational field strength. On Earth, g has a value of 9.81 N/kg.
  2. 2 What is the weight of a mass of 20 kg? W = mg = 20 x 9.81 = 196.2 N
  3. 3 On the Moon, the value of g is much smaller than on Earth , so the same body will have a smaller weight . The value of g on the Moon is about one sixth of g on Earth so the weight will be ⅙ of the weight on Earth. So the mass of a body doesn’t change when the body is moved from the Earth to the Moon but its weight changes.
  4. 4 If weight is the only force acting on a body, then we can use the weight to calculate the acceleration when a body is released. What is the acceleration of an apple of mass 0.1 kg which falls from a tree? W = mg = 0.1 x 9.81 = 0.981 N. Now we can calculate the acceleration using a = F/m. (Remember that F=W) so a = 0.981/0.1 = 9.81 m/s2.
  5. 5 Even if we had changed the mass of the apple to 0.2 kg, the acceleration would still be the same! The apples would hit the ground at the same time.

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  1. What affects the Motion of a Trolley on a Runway?

    However, there will be an amount of friction in the actual experiment, so the differences in results of predicted and experimental should be able to be explained by friction, and how this causes heat energy to be lost. Trial experiments: For my trials I was going to do experiments with the height ranging from 10cm up to 50cm in 10cm intervals. However, I discovered that this was impractical to go above 30cm, because the clamp we used to hold the runway up could not hold the runway above 30cm.

    • Word count: 1377
  2. Test the effects of using a parachute of varying surface area on the terminal velocity of a constant mass.

    Here I can also include momentum. Momentum is the mass of an object multiplied by the velocity. This means that if a cat hits you, travelling at 5mph, it would hurt considerably less than if an elephant hit you travelling at the same speed. I can relate this to the path of air particles- if one thousand air particles hit you at a relatively slow speed; they would not exert as much force on you as they would if you were travelling at 70mph. It is important to remember that your hand is pushing back on the air particles- it is just at the slower speed they are able to resist the force applied.

    • Word count: 1107
  3. To investigate the affect a changing slope has on the distance traveled by a toy car.

    The height of the car at the start should therefore be proportional to the distance traveled, frictional forces ignored. PREDICTION: I predict that, assuming no friction on the ramp, distance traveled is proportional to height of car at start, or amount of gravitational potential energy. That is to say when you double the height of the car, you double the distance traveled. As energy cannot be created nor destroyed we see that the friction that produces the heat comes from the kinetic energy of the car, such that The energy that has been converted to heat will reduce the energy going to kinetic energy, bringing the car to a gradual rest.

    • Word count: 1593
  4. A simple Pendulum.

    With L being the length of the string. This leads us to the equation for acceleration of a simple pendulum bob a = -g/L x. These two formulae then give us the formula for a period, this is Where L = length of string from pivot to bob g = acceleration due to gravity T = time of period. This tells me that there are only two variables, that I have direct control over, that can effect the period of the bob. These are the angle, and the length of the string.

    • Word count: 1212
  5. Gaydon Technology Partnership Centre

    by either increasing stiffness or absorbing them.The legal level of noise from a car is 74 dB as above this it would be deemed as noise pollution and also the more noise it makes the less economical the car is as energy is being wasted in vibrations creating the sound waves.This used to have to be tested outdoors but this created a problem as it could only take place on a clear windless day.The �2.7mill chamber is built to replicate a day like this and to simulate an open road or field.This is done by only being semi as noise

    • Word count: 1408
  6. How Weight Affects Friction.

    Trial Results Mass of sled (g) Added Mass (g) Total Mass (g) Frictional Force (N) Reading 1 Reading2 1 Reading 3 Average Friction 95 200 295 0.2 0.2 0.2 0.2 31 200 231 0.1 0.1 0.1 0.1 Diagram Theory Friction is the force that opposes the motion of an object as it slides across a surface. As soon as you try to slide an object across a surface, friction acts upon it. To be able to slide the object, the pushing or pulling force must match the friction force. The force required to move the object is always larger than the force to keep it moving.

    • Word count: 1273
  7. Investigation on ‘The Law of Conservation of Energy’

    This should mean that the energy at the start of our movement and the energy at the end, should be the same. In order to measure the energy I will need to know several key factors: the mass of the trolley, the force of gravity, the height of the trolley at the start of each run, and the velocity at which the trolley is travelling (at the end of the run). We need the velocity at the end of the run, because this will be the moment when all GPE is changed into KE.

    • Word count: 1385
  8. Rubber Band Investigation

    Hopefully this will not be a problem because the rubber band will not reach its limit of elasticiticty until after 10 Newton's of force being applied. Extra Information The Law of elasticity discovered by the English scientist Robert Hooke in 1660, which states that, for relatively small deformations of an object, the displacement or size of the deformation is directly proportional to the deforming force or load. Under these conditions the object returns to its original shape and size upon removal of the load.

    • Word count: 1687
  9. What affects the acceleration of a trolley

    This amount of potential energy would only be achieved in a vacuum, which could only be carried out with special equipment, which we do not have. If this were possible we would see higher speed due to the absence of friction. Factors that could affect this experiment are the following: Angle of the Ramp The experiment could be affected by the angle of the ramp for example a 10� angle could have a higher amount of potential energy than a 3� angle.

    • Word count: 1381
  10. Experiment to investigate the factors affecting the swing of a pendulum.

    In the diagrams above, it can be seen that the longer string has a longer distance to move than the shorter string, hence its period of oscillation will be greater than that of the shorter string. 2. I predict that the period of oscillation will be independent of mass provided the angle of oscillation and the length of the string are constant. This is because the pendulum will always travel the same distance no matter the mass of the weight attached to it. Apparatus: 1. Retort stand and clamp, 2. G-clamp, 3. Metre rule, 4. 80cm string, 5. Stop watch.

    • Word count: 1904
  11. An Investigation into the factors affecting the time period of a simple pendulum

    Set up the apparatus as shown in the diagram below: 2. Pull the pendulum back to the correct, measured angle and release. Time the pendulum for 50 complete swings over the fidutial point. 3. Repeat three times and take average result. 4. Repeat with varying angles per table and repeat three times at each new angle. Take the average result. For the angle experiments, I have decided to set the length of the string to one metre and the mass of the weight to 100g.

    • Word count: 1130
  12. Investigating centripetal force

    We will study how changing F affects the velocity of an object moving in a circle. To do this we will have to keep all of the other variables the same. * Using the same object for each force value will make sure that the mass of the object remains constant. The object used will be a rubber stopper; it will be attached to the end of a piece of string, which passes through a piece of tubing. The ends of the tubing are polished so that friction is reduced and there is little danger of the string fraying.

    • Word count: 1009
  13. Investigating a Rolling Ball

    Potential energy of the ball at the starting point. 7. Kinetic energy of the ball at the end of the track. Instruments to use are:- 1. A metre rule for lengths. 2. A stopwatch for times. 3. A beam balance for masses. Length will be measured in metres. Time will be measured in seconds. Speed will be measured in metres per second. GPE and KE will be measured in Joules. In order to carry out a fair test the same equipment will be used for each measurement, each measurement will be repeated from the same point at least twice.

    • Word count: 1421
  14. Launch Tube Investigation

    Preliminary Height Table Height of launch tube (cm) Length of launch tube (cm) Distance travelled by ball bearing (mm) 22 10 126 121 90 268 266 27 10 129 124 90 292 281 32 10 145 144 90 345 328 From these results I decided to position the launch tube at a height of 32cm from the level of the sand tray, as the results from this height had the highest range so I will notice a larger difference in my results. Next I decided to determine the angle at which to set the tube. I can work out the angle of the tube using trigonometry.

    • Word count: 1230
  15. Investigating Friction

    While this happens, take a reading on the force meter and record in the table (therefore, I can analysis my results and draw graphs, do calculations, etc). Repeat that step several times, each time add another 100g mass to the pile on the block until I have all the forces for 10 different forces. Finally, record all the readings in the table. Method for question 3: I will start up with the metal iron side first (dun have any special reason, just feel like it).

    • Word count: 1252
  16. Acceleration of falling cones Investigation

    On the moon a feather and a golf ball were dropped at the same time, they both hit the surface of the moon at the same time. In any atmosphere when there is a gas or a liquid they initially drop at the same acceleration, encountering a drag force; this increases as it goes faster. The drag force increases until it equals the weight force, the forces are then balanced and it can't go any faster. This is called terminal velocity.

    • Word count: 1242
  17. To find out how increasing the height an object is dropped from, affects its average speed.

    1. Collect equipment (see below) 2. Set up metre stick along table leg 3. Prepare and weigh plasticine b***s, making sure they are spherical 4. Hold the ball with the bottom of the plasticine just above measurement 5. Drop the ball timing it with the stopwatch until the exact moment it hits the floor 6. Record results on a table (not the same table as the table leg (!) (Not funny-ed.) Equipment: Stopwatch x2 Plasticine (2 grams) Weighing scales Metre stick Parachute (plastic carrier bag) Fair Test: I will make sure this is a fair test by using the same size, weight and density plasticine each time.

    • Word count: 1166
  18. Vehicle Anti-lock Braking Systems

    Under these circumstances, friction opposes the movement of the vehicle?s wheels along the road. Therefore, friction decreasing when the vehicle begins to slide means less force is opposing the vehicle?s movement to slow it down, increasing the vehicle?s stopping distance[3]. The driver also becomes unable to steer as the wheels do not have enough grip on the road to turn, meaning the driver cannot veer to avoid collision (figure 1). Image result for abs braking ABS allows vehicles to stop faster whilst still maintain control of the car (the wheel?s do not lock)[4]. The driver is still able to steer by using two braking techniques; threshold and cadence braking.

    • Word count: 1599
  19. Determining Gravity with a Pendulum

    L = distance between pivot point and center of the pendulum (m) g = value of acceleration due to gravity (ms-2) In order to determine the acceleration due to gravity, the equation were to be arranged to g = Equipment * Scissors * Pendulum (approx 300g) * Whiteboard Diagram Hanger * Whiteboard * Texture * Whiteboard Texture Holder * Sticky Tape * 2m String * Stop Watch Method 1. Set up the pivot point location on the whiteboard as shown in the diagram 1.1 in appendix 1 by using the sticky tape to tape the whiteboard diagram hanger onto the magnetic whiteboard marker holder.

    • Word count: 1836
  20. Physics Pendulum Practical. How does the time period vary with length and what is the value of g?

    Time taken for 20 oscillations 2. Value of g (supposed to be constant variable) Manipulation of Variables Controlled or Constant Variables: 1. Bob: We used the same bob for all trials so that all the results acquired are relevant to one bob only. 2. Mass of bob: Since we used the same bob for all trials, the mass of the bob did not change and remained constant for all trials. 3. String used: We used the same string in all trials to maintain accuracy of the data. 4. Amplitude of oscillation: We made sure that in each trial, the initial amplitude of the oscillation remained approximately 15°.

    • Word count: 1189
  21. Report on Newton's laws of motion

    Newton?s main fields were science and mathematics. He created the well-known famous calculus before Leibniz' became popular. On the other hand, Newton's most affective and famous discovery was gravity which states that {the earth's (gravitational pull) pulls objects toward it}. Newton came up with three laws of motion; these laws form the base of the first branch of physics (Classical Mechanics). What is unique about Newton?s laws is that they explain the way objects move and this is done by finding the relationship between force and motion on the macroscopic level. These laws are the reason behind making physics applicable almost all over the universe except for quantum mechanics, the second branch of physics, which focuses more on the motion at a microscopic level.

    • Word count: 1891
  22. Need For Speed: High Speed Trains

    So engineers were needed to devise a train that could travel at very fast speeds while keeping energy consumption as low as possible. The Japanese started the race for faster high speed trains with their ?bullet trains?, the French countered with the TGV, and many other companies came out with their own high speed trains: Acela, Eurostar, and the Shinkansen, among others [3]. The increase in competition benefitted the consumer, the individual needing to get across the continent because now he or she had a choice between different trains, each known for a specific accommodation.

    • Word count: 1310
  23. Rocket Essay. How Do Rockets Work?

    work on studying the air quality, alternative energy, climate changes, and near earth objects, so whenever there?s a typhoon, earthquake, or any other natural disaster, we could known before hand so we can prevent it or reduce the amount of damage done. How Do Rockets Work? The simplest form of a rocket is a chamber enclosing a gas under pressure. A small opening at one end of the chamber which allows the gas to escape, so that the pressure provides a thrust that propels in the opposite direction, and these pressures are hat pushes the rocket along.

    • Word count: 1094
  24. What are the laws of Physics involved in the design of the roller coaster?

    Centripetal Acceleration ? The formula for centripetal acceleration is ? ar = v^2 / r where ar ? acceleration, v ? velocity and r ? radius. This acceleration is caused by the centripetal force which act towards the centre of the loop. 1. 'G' ? forces ? Greater the centripetal acceleration, greater the 'g' forces which represent the gravitational pull on the riders. 1G is the usual force of gravity felt on Earth. When you feel weightless you experience 0G.

    • Word count: 1064
  25. Sources of Energy in the World

    But where does energy come from? Sources of Energy We get our energy from many sources on this planet. These sources can be mainly divided into two categories: Sources of Energy Nonrenewable Energy Renewable Energy Renewable Energy Renewable energy is energy which comes from sources that can be replenished. These sources never die out and there is no pollution when you use them. The most common renewable sources are: 1. Wind Energy: The energy in the wind is harnessed when the wind currents turns the turbine in the windmill. 1. Solar energy: The energy from the sunlight is harnessed through solar cells.

    • Word count: 1244

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