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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. Marked by a teacher

    Physics CourseWork - Terminal Velocity

    3 star(s)

    the results are * The height the cake cases are dropped from * The number of cake cases dropped (so effecting the weight) * The angle at which the cake cases are dropped * The air condition e.g. wind may effect the time The one that I will be changing is the number of cake cases being dropped. Fair Test: I will make this a fair test by � Dropping them all from the same height of 2 metres at the same angle � Dropping each one 6 times and then finding the average � Using the same size and

    • Word count: 829
  2. Marked by a teacher

    Investigate one factor which affects the time taken for a paper cone to fall a known distance.

    3 star(s)

    Apparatus * Two 1 metre rules * Card cone * Stop watch * Angle to surface area conversion sheet The stopwatch is to time how long the card cone takes to fall a set distance. I will find the best distance in my preliminary experiments. Card will be used to drop because that is the only available material and because it is more rigid than paper but not too heavy. In my preliminary experiments I will also find then best position to place the paper clips to hold the card cone in place.

    • Word count: 1245
  3. Marked by a teacher

    Pendulum experiment

    I also need to take into account what factors will affect this experiment. I need to be very careful when calculating the length, and make sure I use a ruler. Method: - Set up equipment as follows; Attach bob to string. Tie the string to the clamp leaving a length of 100cm for it to swing from. Make sure the stopwatch is set to 0 and draw up a table to record the results. - Hold the bob at a right angle from the clamp stand, and let it drop, timing how long it takes to complete one period with the timer.

    • Word count: 704
  4. Peer reviewed

    Investigating factors that affect the bounce height of a squash ball

    5 star(s)

    This means that once the squash ball reaches a certain speed (its constant, or terminal velocity), it will cease to accelerate. Therefore, no additional speed will be acquired, and so the impact force will be the same. This means that once the terminal velocity can be reached, the drop height should no longer affect the bounce height. There are also a number of variables other that could affect the bounce height of a squash ball. In order to make this experiment fair, I need to eliminate any other variables that might affect the results.

    • Word count: 3683
  5. Peer reviewed

    Physics Practical

    4 star(s)

    Lay the line over the pulley, and align the trolley so it will run straight 6. Place the accelerometer behind the trolley so it will record the acceleration by measuring the distance 7. Have the trolley pulled back far enough to allow an accurate reading for the accelerometer and a person at the end to stop it falling from the table 8. Run 5 trials per mass and record the values for acceleration 9. Repeat steps 7-8 for 700g, 800g, 900g, 1000g, 1100g, 1200g, 1300g, 1400g, 1500g Diagram of Investigation trolley fishing line accelerometer pulley bob mass table GLX Data Collection and Processing Table 1: Collection of Data for the acceleration of different masses Mass of trolley (g)

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  6. Peer reviewed

    wind power

    4 star(s)

    Evidently, wind power is dependant on the weather. To make the most of the available wind, wind turbines need to be situated in areas with high and regular wind speeds which tend to be mountainous or near the coast. Transmitters need similar sites and this limits the locations available for turbines. In 1982, the UK's first turbine was built onshore in South Wales by the Central Electricity Generating Board. From the late 80's plans started emerging to build an offshore turbine of the coast of Norfolk in the North Sea.

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    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.

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  8. Peer reviewed

    Aim To investigate the effect of different masses suspended from a spring on the time period of the spring.

    3 star(s)

    Add 100 grams mass to the spring. 6. Displace the 100 gram mass. 7. Release the 100 gram mass and at the same time start the stopwatch. 8. Record the time taken for 10 oscillations. 9. Repeat steps 6 to 8 2 more times to get three total trials. 10. Now add more mass to the spring and repeat steps 6 to 8 with 200 g, 300g, 400g, and 500g. Diagram Raw Data Table Mass (grams) Time taken for 10 Oscillations (seconds)( +/- 0.01 secs)

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    Centripetal Force

    3 star(s)

    When a mass m attached to a thread is whirled around a horizontal circle of radius r, the tension T provides both the centripetal force and a force to support the weight of the mass M. The tension T is given by T = m?2L, where ? is the angular speed of the mass. Procedure: 1. The mass of the rubber bung, m was measured. 2. One end of a 1.5 m length of nylon thread was attached to a rubber bung and the other end is attached through a glass tube, a paper marker and 2 slotted weights. 3.

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  10. Peer reviewed

    Bouncing A Squash Ball Lab Report - Abhirath Singh

    3 star(s)

    Water - 1 liter Variables: Constant - Time of ball in water, height from which the ball is dropped. Independent - Temperature of water. Dependent - Height of bounce. Method: 1. Take an electrical kettle and heat water in it to 65oC (+ 1oC). Measure the temperature using the electronic thermometer to make sure it is 65oC. 2. Pour the water in a beaker, and place a thermometer in the beaker. 3. Place the squash ball in the beaker with water, making sure the whole ball stays submerged. This can be done by using the tongs. 4. As soon as you place the ball in the beaker, start the stop watch.

    • Word count: 941
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    Factors Influencing Resistance of a Wire

    3 star(s)

    This is because when the battery is attached it creates an electric field throughout the substance. This gives the electrons energy to move, as well as the direction to move. As you can see in the diagram above, as electrons pass through a metal they collide with the metal's atoms, (they are now positive ions as some electron(s) were delocalised and therefore the balance between positive and negative was broken) which are in the way. When an atom collides with a positive ion it loses energy, which it can regain from the electric field.

    • Word count: 3094
  12. Peer reviewed

    hook's law

    3 star(s)

    After each 100g has been added I am going to measure the new length of the weights bag strip. I will then note the difference between the length of the strip at the start of the experiment and the length at the end in order to see what permanent damage has been done. To make it a fair test I will use the same types of weights bags and make sure that they are always the same length. I will also try to gently add the weight so that the force with which it landed does not alter the results.

    • Word count: 692
  13. Peer reviewed

    Physics Pendulum

    3 star(s)

    Measure the time for 20 complete swings when the bob is given an amplitude of 4 cm, 6 cm, 8 cm, and 10 cm respectively. Enter your results into table B. 3. Determine the effect on the period of the pendulum when the length of string is altered. Keep the mass of the bob constant, and give the bob the same amplitude of 6 cm in each case, but change the length of the string so that results are obtained for lengths of 10 cm, 20 cm, 30 cm, and 40 cm.

    • Word count: 1283
  14. Peer reviewed

    road accidents

    3 star(s)

    Graph showing road deaths Source: Portugal: light blue line 2. Scientific Aspects 2.1 Cars Each year cars are getting better due to new technologies. Now many cars are starting to incorporate technologies like ABS which do not let cars slip, preventing many accidents. Air Bags also protect people from getting hurt, protecting the body from hitting in a hard surface. Many other scientific aspects are used in cars construction, which contribute to make them more comfortable and safer, reducing road accidents.

    • Word count: 1391
  15. Peer reviewed

    Hookes lab

    3 star(s)

    This is defined as the 'elastic limit' of the spring. The force constant 'k' of a spring is the force needed to cause unit extension, i.e. 5cm. If a force 'F' produces extension 'e' then, k = F e HYPOTHESIS: As seen the Hooke's law states that the extension of a spring is directly proportional to the tension supplied to it. Therefore I predict that as more weights will be added the extension will increase almost proportionately. Therefore I also predict that the graph will be as shown below: The x axis shows the extension produced by the spring, whereas the y axis shows us the stretching force applied to the spring.

    • Word count: 1716
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    investigation of a simple pendulum

    3 star(s)

    We can use the equation, T = 2 ? V L / G Where (T) is Time, (L) is length of string and (G) is the gravity, to calculate the acceleration due to gravity. I predict that the shortest length will produce the smallest time period. This would take place because the torque (force of metal bob (weight) X distance of string) produced would be relatively less, as the length of string (distance) would be smaller. This will also happen because the metal bob will have a lesser distance to travel, to complete an oscillation, due to the shorter length of the string.

    • Word count: 1941
  17. 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
  18. Simple Pendulum Experiment. Aim: To determine the acceleration due to gravity,g, using a simple pendulum.

    The wood blocks were then placed in the clamp and the grip was tightened. The pendulum suspension was made sure to be friction-free so that the wood blocks could provide a point of suspension for the string.

    • Word count: 437
  19. Werner Von Braun and the development of rockets.

    The first rocket in the series was designed in 1933 and blew up on the launching pad during the first test take off. A-2 was approximately 1.4 meters long and 30cm in diameter. An addition of stabilisation gyroscopes was used on A-2. It was concluded that the parachutes on the A-3 rocket caused too much drag, which resulted in the rocket landing relatively close to the original take off site in Peenemunde. The parachute was later on removed, allowing the rocket to travel further before it crashed.

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  20. Factors that affect the period of a pendulum

    Preliminary Two: Angle Metal Bob is dropped from Independent Variable Dependent Variable Control Variables Angle from which the bob is dropped from(continuous) Period of the pendulum (continuous) Diameter of Bob Type of Bob Same person dropping bob Same person stopping stopwatch Height bob is dropped from Results Table Time of Period (seconds) Angle Bob is dropped from Trial 1 Trial 2 Trial 3 Trial 4 Ranges Averages (mean) 90� 1.01 1.02 1.01 - 1.01-1.02 1.01 80� 1.03 1.07 1.04 1.07 1.03-1.07 1.05 70� 1.09 1.02 1.06 1.09 1.02-1.09 1.07 60� 1.13 1.15 1.21 1.21 1.13-1.21 1.18 A This graph clearly shows a negative correlation between the period of a pendulum and the angle from which the bob was dropped.

    • Word count: 2148
  21. Physics Coursework - car braking investigation.

    By analysing the table and bar chart, I can see that for every 10mph the car goes, the thinking distance increases by 3m metres. This shows that the reactions of the driver have decreased. The braking distance also increases. Therefore, this means that the overall stopping distance also increases, meaning that a collision is more likely. Stopping distance can be affected by many factors, the main ones being the speed the car is travelling at, the use of a mobile phone, drink-driving and wet weather.

    • Word count: 1232
  22. Free essay

    Investigation into the motion of a cart down a track

    Errors Although one thing we could not fully remove was the chance of human error, For example since we were timing on a stopwatch operated by human hands there is the chance that the person timing the cart will be record the result wrong. Safety To make the experiment safe we also employed a variety of safety measures such as: 1. We placed a "stopper" at the end of the track so the cart would't fly off and hit something or someone 2.

    • Word count: 1017
  23. To investigate how the height of a ramp affects the speed of a trolley

    I also think that the relationship between the height of the ramp and the change in speed will be directly proportional. What we done 1.Firstly I gathered all my equipment that I needed 2.I then assembled the ramp to the first height (10 cm) 3.I made sure the stop clock was ready to start, meaning that it was set on 00:00.00 4.Next I placed the trolley on the ramp at the black 5.Then I Presses the stop clock when the trolley was released.

    • Word count: 1290
  24. 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
  25. invetigation:Principle of conservation of energy in terms pe and ke

    An object of mass, m, at a height, h, above the ground has potential energy PE=mgh. If the object falls, its potential energy decreases. As it falls, its velocity increases, so its kinetic energy (KE= 1/2 mv2) also increases. By the law of conservation of energy, the sum of the potential energy and the kinetic energy must remain the same. It follows that the sum of the changes in potential and kinetic energy must equal to zero:?PE=? KE? mgh =1/2 mv�In this experiment, in order to prove that the total gravitational potential energy is converted to kinetic energy, hence abiding

    • Word count: 1342

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