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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 of Rollercoasters

    4 star(s)

    Newton put forth a variety of laws that explain why objects move (or don't move) as they do. Newton's first law is a restatement of what Galileo had already described that force acting on a body determines acceleration, not velocity. This insight lead to Newton's First Law- an object at rest will stay at rest and an object in motion will stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

    • Word count: 2587
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    Physics Investigation: The effect of speed on braking distance

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    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
  3. Marked by a teacher

    Parachute Coursework

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    So using a larger weight will mean it will reach its terminal velocity slower. Plan Apparatus Bin liner 4 equal lengths of string 10 one gram weights of plastercine Stopwatch- to measure the time it takes for the parachute to reach the ground Meter ruler- to measure the distance the parachute has fallen To make it a fair test I repeated the test 3 times and made an average of my results. Pre-test As we had no idea on what size of parachute area, weight of plastercine or length of string to use we had to do a pre-test, we tested each variable.

    • Word count: 796
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    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
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    The aim of this experiment was to compare the elasticity of arteries and vein tissue and to identify how the structure of blood vessels relates to their functions.

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    Based on the above scientific knowledge it was believed that the arteries may well have more elastic fibres than the veins, as arteries have a high pressure, which needs to be kept constant for blood to reach the extremes of the body. Veins will therefore have less elastic fibres due to their lower pressure environment. This leads to the establishment of a hypothesis that arteries have more elastic fibres than veins. Also due to the artery having a smaller lumen (relative to its diameter)

    • Word count: 1703
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    Investigating a Cantilever.

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    Also a perfect length so that the cantilever is safe and isn't likely to break. Length (mm) Mass (g) Start Height (mm) Finish Height (mm) Deflection (mm) 100 500 831 831 0 200 500 831 828 3 300 500 831 823 8 400 500 831 813 18 500 500 831 789 42 600 500 828 759 75 700 500 825 716 109 These are results of our preliminary test From these results we decided that 500mm was the optimum length of the cantilever.

    • Word count: 1032
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    To investigate the factors that affect the stopping distance of a catapulted margarine tub. In this experiment, I will be concentrating on the effect that varying the mass of the catapulted tub has on its stopping distance (sd.).

    4 star(s)

    When the elastic band is pulled back then it has Elastic Potential Energy (EPE) which is changed to kinetic energy (KE) when the band is released. If the elastic band is pulled back further then it has a higher level of EPE to start off with, so when it is released, it will have more KE and the margarine tub will go further before stopping. If the margarine tub was on a sloped surface, going down, then the same amount of EPE and KE would take it further than it would on a flat surface because the KE would turn into GPE (Gravitational Potential Energy)

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    The Simple Pendulum Experiment

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    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
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    Physics research study - vehicle safety and braking distances

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    millions of pounds promoting the awareness of drunk driving (40% of all traffic fatalities are because of alcohol And to combat this they have introduced drinking limits. Being under the influence - even legally - seriously alters how well you can judge hazards. Your body also moves less accurately. Late or missed braking results. Also is the driver is distracted in any way or is not fully concentrating this increases the thinking distance. Poor visibility is also a common factor this delays the time before the driver realises he needs to apply the breaks.

    • Word count: 959
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    Do Elastic Bands Obey Hooke Law

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    of the rubber band * Rubber band Things that will change due to the experiment; * Length of rubber band Results; Length of Rubber Band (cm) Weight (G) Weight (N) 5 0 0 7.8 50 0.5 9.3 100 1 11.1 150 1.5 14.6 200 2 18.9 250 2.5 22.5 300 3 25.6 350 3.5 31.5 400 4 31.9 450 4.5 33.6 500 5 34.9 550 5.5 36.7 600 6 38.5 650 6.5 39.2 700 7 40.4 750 7.5 41.6 800 8

    • Word count: 551
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    Additional Science - What affects the period of a pendulum?

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    - 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
  12. Marked by a teacher

    Investigate the relationship between GPE (Gravitational Potential Energy) and KE (Kinetic Energy) for a trolley or ball rolling down the slope.

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    makes it more likely for my results to be more accurate. So the question I investigation is, Is there a relationship between Velocity (V) and Height (H). To investigate this I used the following equipment: Ramp- To roll the trolley off of, vary the height of the surface. Two light gates- To pick up the readings from point A to B Data Logger- Connected to the two light gates, to show readings Metre Ruler- To measure the height on the slope/ramp Standing Clamps-To holding the two light gates and slope in place.

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  13. Marked by a teacher

    Physics Pendulum Experiment

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    a simple pendulum swinging back and forth. A pendulum is able to operate when the mass is lifted to an angle and then released, and by doing this, the pendulum will be using Gravitational Potential Energy. In my experiment, I am going to find out if there is a relationship between the mass of the weights, and the time taken for a full oscillation. I predict, that as the mass increases, the time taken for a full oscillation will increase, as there will be more weight. Method The experiment was setup on the pendulum at a fixed length.

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  14. Marked by a teacher

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

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    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
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    Biology Investigation What affects the crawling speed of maggots?

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    This kind of natural phenomenon is apparent especially in evolution of species. For example, for a cheetah to be able to survive in the wild, it must be fast so it can catch it's pray and outrun predators. But this is not the only thing the cheetah needs for survival; it must also have strength (mass) for it to be able to fight other cheetahs for mates or territory. If the cheetah was not large enough it would lose fights and may never produce any cubs and would not be able to fight for territory, if the cheetah did not have sufficient mass or strength, it would not survive and its chain would be broken.

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    Stopping distances of toy cars travelling down a ramp

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    In the first experiment I will keep the height of the ramp at 10cm so that height does not affect the stopping distance. Then the car will be placed at the top of the ramp and released, not pushed. The weight of the car will increase from 30g, the weight of the car, to 80g in 10g intervals. Six results will therefore be obtained and the car will be released from the top of the ramp three times on each weight to gain an average and hence fairer and more accurate results.

    • Word count: 1092
  17. Marked by a teacher

    I have chosen to investigate how the amount of force used to propel the margarine tub will affect the speed. I predict that as the force used to

    3 star(s)

    I predict that as the force used to draw back the elastic band increases, so will the speed at which the margarine tub travels.

    • Word count: 290
  18. Marked by a teacher

    Investigating how the Length of a Pendulum affects its Period

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    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
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    Experiment Report: Studying a simple harmonic oscillator.

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    During the oscillation, the pendulum bob accelerated and then decelerated when it was approaching its highest position. The acceleration of the bob was always pointing towards its equilibrium position. 3. The two most widely spaced dots were marked on the tape - the zero position of the pendulum bob was found. 4. Every dot on the tape was marked from the zero position. The displacements of these points from the zero position were measured and the corresponding time was worked out. Time interval between two successive dots = 0.02 s. 5. These data was plotted on a displacement-time (x-t)

    • Word count: 1482
  20. Marked by a teacher

    Investigating a factor which can affect the period of a pendulum.

    3 star(s)

    When the bob is above the point of natural suspension, it is going against the natural gravitation force and thus, gains Gravitation Potential Energy. When the bob is drawn and released at whatever angle, the gravitational force acts upon it by moving the pendulum down, towards the point where it is vertically suspended at rest. From this, we can say that as the pendulum is released, its Gravitational Potential Energy is converted to Kinetic energy in order for the pendulum to move.

    • Word count: 1991
  21. Marked by a teacher

    How does the height of a ball drop affect the bounce?

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    * Temperature: The temperature of the ball will affect the speed that the air molecules move, and therefore changing the pressure within the ball and the bounce upon impact with the surface. * Colour: The colour may affect the bounce of ball as certain colours attract more sunlight and the more light there is, the more heat there is and this would consequently change the pressure within the ball. For my preliminary work I conducted a series of tests to work out the best variables to change for my experiment.

    • Word count: 1064
  22. Marked by a teacher

    Friction Between two surfaces

    3 star(s)

    There are two types of friction static and sliding. Sliding friction is the frictional force, which exists between two adjacent surfaces, which are in relative motion, and is usually slightly less than the limiting frictional force between the surfaces. Static friction is the force of friction present when there is no motion between the two surfaces in contact. After looking up experiments to show that there are two types of friction in A-level physics - Roger Muncaster not only did I find and experiment but it show another factor the coefficient of limiting friction.

    • Word count: 1760
  23. Marked by a teacher

    I aim to find out if the mass of an object affects the speed at which it falls.

    3 star(s)

    According to Vincenzo Viviani Galileo demonstrated his conclusions by dropping weights from the leaning tower of Pisa." I will drop the object, which will be a small container, from a height of 30cm. I will measure the speed of the object using a light gate, which will make my results accurate to two decimal places. I will use sand to increase the mass of my object because this will be very accurate and it will not alter the shape of the object. After my preliminary test I concluded that 30cm would be the best height to drop the container from.

    • Word count: 1122
  24. Marked by a teacher

    The aim of this experiment is to investigate what effect the surface area of a parachute has on the terminal velocity of the parachute.

    3 star(s)

    When the air resistance and the velocity balance out, maximum velocity is achieved and there is no further acceleration, this is called "Terminal Velocity" Variables: There are different variables that can be changed in this experiment. Variable Method How will it affect the terminal velocity? 1. Surface Area This variable can be changed by making a large parachute at first and then cutting the size down. Terminal velocity should be larger as the Surface Area becomes smaller. This should be because there will be less Air Resistance when there is less of the parachute to trap the air.

    • Word count: 656
  25. Marked by a teacher

    To investigate elastic bands, whether they follow Hookes Law.

    3 star(s)

    I will only do this for the 1st and 2nd experiment. Safety: * I will have to wear goggles so when the elastic band snaps it won't flick in my eye. * I will use a G Clamp so the equipment won't fall. * I won't put my feet under the table as the weights might fall. Fair Test: I will make this a fair test by: * I will make the results accurate.

    • Word count: 547

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