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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. For this experiment, I and my partner decided to find out how different mass can alternate the average speed of the parachute.

    2) We add sand to 5 zip lock bags, to a certain mass. For example: 5g, 30g, 15g etc. and we left one empty 3) Then we cut the long piece of string into 5 equal parts, using a ruler to measure 4) After that we made a hole in each zip lock bag with a scissor, this is for the string to get through the zip lock bag. 5) After that we put the string through the hole of each zip lock bag and through the holes of the plastic bag , and securing it with a knot 6)

    • Word count: 813
  2. My aim is to investigate how the temperature has an effect on the height of the bounce of a squash ball.

    The hotter the solid becomes, the more they vibrate. This causes the solid to expand slightly when heated. Solids cannot be compressed because the molecules are already packed very close together. When the solid hits the ground the atoms push each other away forcing the ball to bounce higher. So this is another factor in consideration. AI M My aim is to investigate how the temperature has an effect on the height of the bounce of a squash ball. Equipment: � Meter rule - to make sure the drop height is 1m and to measure the bounce height � Squash ball - to be able to conduct the experiment

    • Word count: 3627
  3. In this experiment I am going to find out how and why the temperatures of a squash ball affect its rebound height.

    APPARATUS * Squash balls( 1 or 2) * 2 metre rules * Beaker * Source of heat ( kettle or Bunsen burner) * Water * Thermometer * A pair of Tongs My results Temperature Of the ball (�C) Bounce height (cm) Test 1 Test 2 Test 3 Average 27 25 27 28 26.67 32 27 27 28 27.33 37 32 32 33 32.33 42 30 33 34 32.33 47 40 40 41 40.33 52 40 41 42 41 57 39 43 45 42.33 The table above shows the raw data collected from my investigation.

    • Word count: 1899
  4. 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
  5. Free essay

    Science Prac 1

    it will remain at rest without the application of an external or unbalanced force (exploration.grc.nasa.gov). Newton's second law stated that: The relationship between an object's mass, its acceleration and the applied force is: F= ma (csep10.phys.utk.edu). In other words "heavy objects require more force to move the same distance as lighter objects" (teachertech.rice.edu). Newton's third law stated that: For every action there is an equal and opposite reaction (csep10.phys.utk.edu). "This means that for every force there is a reaction force that is equal in size but in the opposite direction. That is to say that when an object pushes another object it gets pushed back in the opposite direction equally as hard" (teachertech.rice.edu).

    • Word count: 1992
  6. Physics Coursework

    The gradient between points nineteen centimetres on the average point and twenty centimetres on the average point is almost zero. This is because the car has almost reached its terminal velocity and can not travel much further even if the car has more gravitational potential energy. The graph shows us that the gradient on the left side of the graph is larger them the gradient on the right side of the graph. This is because the gravitational potential energy is larger, meaning that there is more kinetic energy so that the car can travel further because there is more energy to counteract the friction of the ground.

    • Word count: 1684
  7. 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.

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  8. 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
  9. How does the viscosity of a liquid affect the flow of a sphere through it?

    Viscosity of various fluids Fluid Viscosity (Pa s) Hydrogen 8.4x10-6 Air 17.4x10-6 Xenon 2.12x10-5 (Room temperature) Blood 3x10-3 Castor oil 0.985 Glycerol 1.5 Mercury 1.5x10-3 Water 8.94x10-4 Up thrust (U) When an object is fully or partially immersed in a fluid, the fluid exerts a force on the object upwards. Archimedes Principle The up thrust acting on an object that is partially or fully immersed in a fluid, is equal to the weight of the displaced liquid. Up thrust= the upward force on the object. According to Archimedes Principle, Up thrust= Weight of the displaced liquid.

    • Word count: 1193
  10. Approximate Stopping Distances

    Although the thinking distance is a smaller portion of the overall stopping distance than the braking distance; it is still a huge amount, at 70 mph the thinking distance is 70 ft even before you slam down on the brakes. The graph shows that the faster the speed of the vehicle the higher the overall stopping distance is, this is because when the vehicle is travelling at 20 mph the braking distance is 20 ft. however when the vehicle is travelling at a higher speed for example at 40 mph the braking distance is 80 ft, this means that as the speed of the vehicle increases the braking distance also increases but not at a consistent rate.

    • Word count: 5066
  11. Physics Lab Relative Density

    Drawing Pin Experiment * Triple beam balance * 10ml Class B measuring cylinder * 10 drawing pins * displacement can * 250ml beaker Diagram- Diagrams Showing setup of the Cork Bung Experiment- Diagram showing the setup of the pins experiment- Method- Cork Bung Experiment 1. The displacement can was filled to the spout 2. The cork bung was tied to the sinker and placed in the displacement can 3. The water displaced water was collected in the 250ml beaker and then transferred to the 100ml measuring cylinder 4.

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  12. Force and Extension Experiment

    Using different springs might have affected the limit of proportionality, which is why I performed the experiment four times, with two different springs.

    • Word count: 215
  13. To determine the elasticity of an elastic band by applying Hookes law.

    A mass of 20 g was then attached to the bottom of the elastic band allowing it to be hanged in air and the new length is noted. 4) The new length is then subtracted from the original one to get the extension. 5) Steps 3 and 4 are repeated variously for with new loads each time. 6) The above step is then repeated but by removing loads instead of adding then 7)

    • Word count: 573
  14. Physics Lab - Conservation of momentum

    * Meter rule � 0.05cm - to measure the distance the bodies travel, to eventually calculate the momentum. * Pen & paper - to note down the readings. * Metallic track - to slide the carts on, to provide an almost friction-less surface. * Electronic balance �0.01g - to measure the mass of the bodies. Method / procedure #1 1. Measure the mass of the two carts using an electronic balance and note down the readings. 2. Place the two carts on the track, Cart 1 at the start and Cart 2 approximately in the middle of the track, facing the same direction.

    • Word count: 1900
  15. Additional Science

    Angle it is dropped (degrees) 1st time (secs) 2nd time (secs) 3rd time (secs) 4th time (secs) 5th time (secs) 6th time (secs) 7th time (secs) Average (to 2.d.p) 180 1.25 1.10 1.32 1.32 1.42 1.10 1.41 1.34 170 1.29 1.27 1.28 1.24 1.09 1.24 1.25 1.26 160 1.22 1.22 1.28 1.25 1.25 1.27 1.19 1.24 150 1.16 1.15 1.16 1.26 1.20 1.22 1.14 1.18 Angle it is dropped (degrees) Spearman's rank Average times (seconds & to 2.d.p) Spearman's rank d^2 180 1 1.34 1 0 170 2 1.26 2 0 160 3 1.24 3 0 150 4 1.18 4 0 ?d�= 0 6 x 0 = 0 n(n�-1)

    • Word count: 3829
  16. 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
  17. Speed Of trolley

    Potential energy is the reason for the increase of velocity. When the slope is steeper, the height of the runway increases. When the height increases the potential energy of the trolley also increases. All the potential energy is converted into kinetic energy during the motion of the trolley. At the bottom there is no potential energy so potential energy equals to 0. At the top potential energy is used not kinetic energy, so there is no kinetic energy. This means at the top kinetic energy is equal to 0.

    • Word count: 1913
  18. Aim: To investigate the rate of cooling of water in two different containers.

    Continue this recording every thirty seconds. 7. Stop after 10 minutes. 8. At the end observe the difference in the total decrease in temperature. Modifications in procedure: ==> The readings were simultaneously recorded every 30 seconds for direct comparison. ==> The readings were taken for ten minutes. ==> Both the containers were exposed to the same material, wood, which had the same insulating effect on the containers. ==> Two sets of readings for each container were taken. Experimental setup: Maintaining Fair test: ==> The volume of water was kept constant.

    • Word count: 626
  19. Density of irregular object

    Lower the rock into the water. 4. Observe and record observations. 5. Use balance to find mass of irregular object (rock). 6. Process all data collected. 7. Clean up work area.

    • Word count: 248
  20. Research questions: what determines the amount of energy given off by a Bunsen burner? Is there any correlation between the colour of the Bunsen flame and the amount of energy it supplies? How exactly is the Bunsen burner supplying energy?

    Measure the final temperature of the water. 8) Record all data Collected. 9) Process Data collected in an appropriate manner. 10) Clean up the work area. Literary review: The specific heat capacity of a substance, according to answers. Com is the amount of heat energy that must be added to, or removed from, a unit of mass of a given substance to change its temperature by 1�C.

    • Word count: 575
  21. Simple pendulum

    2. Bob 3. Stand 4. Timer Method * I will set up the simple (shorter) pendulum on the stand * I will pull bob, backwards with my hands * I will release the bob from a angle of 45 Degrees. * Remember the angle of release has to always stay the same. * I will let it complete three periods, which will be timed with a stopwatch * Then i will calculate tge average for that length * Then i will repeat the experiment but with a longer length of thread. And repeat the experiment 6 x with 6 different length of wires.

    • Word count: 800
  22. 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
  23. Energy Conversion

    The table below shows the data that I collected from the practical experiment which I carried in the classroom: Now that I have collected my data I am going to calculate the rate of heat transfer by using the following formulas: Energy input = ITV I = Current T = Time V = Volt Energy output = mC?T m = Mass C = Specific heat capacity ?T = Temperature change Electricity to heat Energy input: I = 5 � T= 302 � V=7.5 = 11325 Energy input = 11325 (J)

    • Word count: 839
  24. How does speed affect stopping distance? I chose to release a car from the top of a hill and let it roll down, as the height of the ramp increases the speed of the car increases.

    Basically as the speed increases the stopping distance increases. However in my graph 'speed v stopping distance' it starts with speed increasing in a straight line and then the line becomes curved as if it would eventually flatten out as the speed increases. From the 'speed^2 v stopping distance' graph a can see that there is a clear relationship between the two results basically as the height of the ramp increases so does the stopping distance.

    • Word count: 417
  25. Parachutes Lab

    In this experiment we will explore the factor of surface area of the parachute, which affects the way a parachute falls. Variables: Constant Variable - Distance traveled by parachutes & weigh of the plasticine. Independent Variable - Surface area of parachute. Dependent Variable - Time taken by parachute to fall & speed of the parachute. Materials: 1. Polythene sheets - minimum size = 25cm x 25cm - 5 sheets. 2. Thin string - Length = 1400cm. 3. Meter Rule. 4.

    • Word count: 1031

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