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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.

  • Marked by Teachers essays 28
  • Peer Reviewed essays 14
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  1. Marked by a teacher

    Physics Investigation: The effect of speed on braking distance

    4 star(s)

    E.g., ice is more 'slippery' than a rough surface because it is very smooth, and therefore exerts less friction on the object travelling on it. The friction force gradually converts the kinetic energy of the moving object into different forms of energy such as sound and heat, until the object's kinetic energy is reduced to zero - hence why it always stops eventually. The longer it takes for the object to have its kinetic energy reduced to zero, the longer the braking distance.

    • Word count: 2704
  2. Marked by a teacher

    The purpose of this experiment is to see what factors affect the period of one complete oscillation of a simple pendulum.

    4 star(s)

    is the only force making the mass move and not gravitational potential energy (GPE). I will test the extremes of these factors as I can assume that if they have any effect on the period of oscillation it will become obvious. To make sure my results are accurate enough to allow for any anomalies I will repeat the experiment 2 times for each test. To keep the results as accurate as possible I will measure the period of 10 oscillations and only use one decimal place to allow for my reaction time. Prediction I predict that the factor that effects the swing time in the pendulum experiment will be the length.

    • Word count: 2115
  3. Marked by a teacher

    The Simple Pendulum Experiment

    4 star(s)

    After gaining the results of this experiment, I will be able to plan my main experiment more thoroughly. Preliminary Experiment The diagram below shows a brief set-up of the simple pendulum experiment The pendulum (3) will be held by a clamp stand (1) which will be placed on a work bench table (2) Fig. 1: Simple Pendulum Experiment Set-up Figure 2 I will use a digital chronometer (4), which is accurate to within �0.005s to measure the time of the oscillation, and a ruler (accurate to within �0.0005m)

    • Word count: 2780
  4. Marked by a teacher

    Additional Science - What affects the period of a pendulum?

    3 star(s)

    - Use the same ruler throughout the experiments as another ruler could be different by a few millimetres. - Drop the ball bearing from the same height and angle, unless for the experiment where I am testing to see how a change in angle and height affects the period. EQUIPMENT: - 1 retort stand - Ball of string - Metal ball bearings - Protractor - Stop watch - Electronic scaled - Scissors - 30cm ruler - Elastic bands - Cello tape PRELIMINARIES: Preliminary Test #1: In this preliminary I am experimenting to see how the length of the string affects the time period of the pendulum.

    • Word count: 2955
  5. Marked by a teacher

    Which factors affect the time period of the swing of a pendulum?

    3 star(s)

    two times. I will conduct a preliminary experiment in order for me to establish what the general trend of results would be and to help me perform a more accurate final experiment. In my preliminary experiment I will be varying 2 factors, one being the length of string on the pendulum and another being the angle that I drop the pendulum from. I am varying the angle that I drop the pendulum from to investigate whether this has any effect on the time rate of a swing of a pendulum, hence, I will be able to implement my findings into my final experiment.

    • Word count: 2264
  6. Marked by a teacher

    Investigating how the Length of a Pendulum affects its Period

    3 star(s)

    Amplitude (or the angle at which the bob is released at) does not matter, as proved earlier. I must also ensure that the corks holding the string are held securely or else the string could slip through and then the length would change. When I do the experiment I will firstly release the ball and then wait till I am used to the speed of the swing and then start timing. But I shall not just time one period, as this would increase the chance of inaccuracies due to my reaction times.

    • Word count: 2024
  7. Peer reviewed

    length of a simple pendulum affects the time

    4 star(s)

    As the pendulum falls the potential energy is transferred to kinetic energy. The speed increases as the pendulum falls and reaches a maximum at the bottom of the swing. Here the speed and kinetic energy are a maximum, and the potential energy is a minimum. As the pendulum rises the kinetic energy is transferred back to potential energy. The speed of the pendulum decreases and falls to zero as it reaches the top of its swing, with the potential energy a maximum again. A small amount of energy is lost due to air resistance as the pendulum swings.

    • Word count: 2341
  8. Peer reviewed

    Investigate the factors which affect the period of one swing (oscillation) of a simple pendulum.

    3 star(s)

    When the length is increased, the time is increased. When length is 0.4m, time period is 1.269s. This tells us that when the length is increased, the time period is increased. 2. Angle of release A simple pendulum is only a weight known as a "bob" hung from a string. When the bob is lifted, the pendulum gains potential gravitational energy, as it is acting against the force. Therefore, the angle, which would raise the height, would give the bob more gravitational energy (up to 90�).

    • Word count: 2067
  9. My investigation is about how the number of paperclips added onto a paper spinner affects the time taken for the spinner to fall from a height of 3m.

    Spinner A spinner is a bit like a helicopter but the blades are quite different. On a helicopter the rotor blades are curved at the top and flat at the bottom, this causes air to flow faster over the top so there is more pressure underneath the blades. This high pressure underneath the blades allows the helicopter to take off. A spinner has wings that are flat top and bottom, so there is equal pressure, so it does not take off, but due to air resistance the flat surface of the spinner has an upward force slowing it down.

    • Word count: 2751
  10. Acceleration due to gravity lab

    Methods and Materials Materials To perform this experiment efficiently and safely, the appropriate materials are required. These materials are a metre stick, a staircase or area in which enough height is provided to drop a ball, a standard sized basketball, and a camera or video recording device. Method To get started with this experiment, proceed to a staircase or the area of enough height to perform the experiment. Place a metre stick along the side of the staircase where it is in clear view on the camera.

    • Word count: 2445
  11. Resistance coursework

    Aim I am going to be studying the resistance of wire. The purpose of this investigation is to see how length and thickness of wire affect the dependent variable, resistance. I want to find out how the resistance of a wire is affected by the length of the wire. I will do this by doing my experiment, see below. Preliminary: Aim: For my preliminary test I am going to investigate what factors affect the resistance of a wire. And decide what equipment I want to use and why. There are three main factors which affect the resistance of a wire: The material of the wire.

    • Word count: 2190
  12. The Physics of Sailing

    and is used by advanced sailors to increase the boat's speed in specific instances. Sailboats don't have a steering wheel; instead they have a rudder which is controlled by a tiller. When the tiller is pushed to the right, the rudder will move to the left causing the boat to turn left. Large boats have a keel, while small boats have either a centerboard (cannot be physically removed from the boat) or a daggerboard (can be easily removed from the boat). Regardless of the type of boat, these sharp blades project from the bottom of the boat into the water and stop slide slipping - a phenomenon that will be explained later on.

    • Word count: 2500
  13. Fly with physics

    by Leonardo and his contemporaries one can cull out some rather interesting facts that attest to the fact that YES his machines did work and Leonardo did fly"(Dann). Throughout the world there have been several possible candidates who may have invented the first airplane that flies using the principles that airplanes use today. According to ThinkQuest the first airplane was a non-motorized flying machine, invented by Sir George Cayel, called a glider. His first glider didn't have passengers or a pilot because it was too small for anyone to fit in it.

    • Word count: 2238
  14. Hooke's Law Lab

    5cm. If a force 'F' produces extension 'e' then, k = F e (Sourced from: Microsoft (r) Encarta (r) Reference Library 2005. (c) 1993-2004 Microsoft Corporation. All rights reserved.) HYPOTHESIS: Hooke's Law states that the extension produced by the spring is directly proportional to the tension force applied to it. Therefore, in this experiment I hypothesize that the extension produced by the spring will increase as more weights are added. The graph for this extension will be as follows: The Y-Axis shows the stretching force 'F' and the X-Axis represents the extension produced by the spring. VARIABLES: Constant: - surroundings - equipment used - Independent: - Weights added (force applied)

    • Word count: 2259
  15. Physics - how the launch height affects the horizontal distance a ski jumper travels from the launch ramp

    Shown in diagram (1) bellow. To make measuring more accurate we used a setsquare to make sure that we knew we were measuring from exactly the right point. Shown in diagram (2) bellow. We measured the horizontal distance from the closest point to the table; we measured the value to the nearest 'mm', each time to make our results consistent. Sand Type: In our experiment the ball would run off the ramp and land in the tray of sand and we measured the horizontal distance travelled by the ball was measured by the crater in the sand.

    • Word count: 2440
  16. Trolly Experiment

    To reduce the fiction of the wheel axis on the trolley, I have sprayed it with a lubricant (WD40). The results I have been given are as follows: Distance to Light Gate (m) Velocity (m/s) 1st go 2nd go 3rd go Mean Velocity 0.8 0.565 0.556 0.556 0.559 0.7 0.532 0.518 0.525 0.525 0.6 0.487 0.484 0.481 0.484 0.5 0.449 0.436 0.437 0.441 0.4 0.395 0.390 0.393 0.393 0.3 0.339 0.338 0.339 0.339 0.2 0.277 0.277 0.274 0.276 0.1 0.186 0.191 0.190 0.189 I have decided to make a preliminary graph to show my expected results. The graph above shows that as the slope distance increases the velocity of the trolley must increase.

    • Word count: 2212
  17. Efficiency of energy transfer on a rolling object

    I will need to find out the efficiency of the energy transfer from G.P.E to K.E. The formula is: Efficiency = Useful energy transferred (KE) x 100 Total energy supplied (GPE) To work this out I need to know the G.P.E the marble has at the top (therefore the maximum G.P.E) and the amount of K.E the marble has at the end of the slope (therefore the max. K.E). We can find G.P.E by using the following formula: GPE = mgh m = the mass of the object in Kilograms g = the acceleration due to gravity in metres per second squared h = the height in metres.

    • Word count: 2203
  18. My objective in this experiment is to find out how a spring varies in length with added load. I also want to witness Hookes Law in action, and I want to observe the behaviour of the spring/s even after the load added causes the stress in the spring to

    tension and/or compression) have been removed. Materials which have this ability are elastic; those which do not have this ability are considered plastic. This always happens when the distorting force is below a certain size (which is different for each material). This point where the body will no longer return to its original shape/size (due to the distorting force becoming too large) is known as the elastic limit (which differs from material to material). As long as the distorting force is below this size, the body that is under the external forces will always return to its original shape.

    • Word count: 2707
  19. Determination of the Acceleration due to Gravity on the Earth’s Surface

    In Figure 1, as the velocity increases, the air resistance arrow would grow, showing that the air resistance would increase as well. Eventually, it will equal the weight arrow and the air resistance will equal the weight. This would mean there would be no more acceleration, and the body will have reached a terminal velocity. In a vacuum, there would be no air resistance, so the body will not decrease its acceleration. Therefore, this would give the most accurate value for standard gravity.

    • Word count: 2042

    Whenever an object is on a horizontal surface, there'll always be a reaction force pushing upwards, supporting the object. The total reaction force will be equal and opposite of the weight. In the above diagram the object is not on a horizontal surface there is no reaction force pushing upwards, therefore the resultant forces is greatest when the slope is vertical. Variables The two changing variables in this experiment are: * The speed of the ball * The height of the ramp.

    • Word count: 2034
  21. biomechanics

    Like the wind blowing some one over or friction grinding a car to a stop. In sport you could relate this to a rugby player tackling another player. Impulse - "Impulse is a measure of what is required to change the motion of an object and is a product of the force applied and the time over which this force is applied." http://www.quintic.com/education/case_studies/impulse.htm The equation for impulse is force x time = impulse. Impulse is the change in momentum. In sport it is used to change direction at speed which is agility. In basketball a player will produce a force to change his direction and the faster he does this the faster the impulse is.

    • Word count: 2132
  22. The Pendulum

    We have decided to go up in fives i.e. 5, 10, 15 etc... 2) Then we have to draw up a table o record all f our results. 3) Next we have to collect all our apparatus. 4) Firstly, we will measure a piece of string to the length required, plus a bit for excess to tie around the weight ball etc... 5) We then will set up our clamp and attach the string to the clamp attachment and in turn, attach the weight ball to the string. 6) After all is set up, we will need to wind up the string around the clamp to the lowest measurement ready to begin the experiment.

    • Word count: 2762
  23. To Investigate a Single Factor that Affects the Speed of an Object at the End of a Runway

    And conservation of energy states mgh= 1/2mv (mgh =gpe). Mass will have no effect because final speed only depends on 2xgxh, not mass. Predicted Values The predicted values are worked out by doing a simple equation: V(2gh) (=V... final speed) e.g.: V(2x10x0.10). The results that I get at the end of this experiment should be the same or similar to the predicted values. Height (m) Predicted speed at the end of the ramp (m/s) 0.10 1.41 0.20 2.00 0.30 2.45 0.40 2.83 0.50 3.16 This table shows how the height will affect the speed of the object at the end of the ramp.

    • Word count: 2570
  24. science pendulum experiment

    Gravity is another factor which will affect the pendulum. Gravity is also the reason why the pendulum moves in the way. Without gravity, the pendulum would not swing as it could stay in the air forever. Gravity remains the same on each object, so this shouldn't be a problem. After going through the possible factors that could affect the oscillation of a pendulum, I have decided to do some preliminary work on the length of the string, and the Angle of release.

    • Word count: 2354
  25. What is the effect of mass on friction?

    The mass is then placed onto the first surface and the force meter hooked onto it. Refer to the pilot test to know which force meter would be more suitable at this stage. The block is then pulled along the surface at constant speed and the reading on the force meter should be recorded in the table of results. Repeat this reading two or three times to increase its reliability and then calculate an average of all the readings. Remember to include the repeat readings and the average in your table of results. The experiment should then be set up again using the same block of wood and the same surface but by adding a mass onto the block thus increasing its weight.

    • Word count: 2750

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