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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

    Parachute Coursework

    4 star(s)

    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
  2. Marked by a teacher

    Do Elastic Bands Obey Hooke Law

    3 star(s)

    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
  3. 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
  4. 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
  5. 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
  6. 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
  7. 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
  8. 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)

    • Word count: 823
  9. 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)

    • Word count: 862
  10. Peer reviewed

    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.

    • Word count: 691
  11. 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
  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. 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
  14. 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.

    • Word count: 732
  15. 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
  16. 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
  17. 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
  18. 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
  19. 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
  20. 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
  21. 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
  22. 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
  23. Testing the bouncing efficiency of thre different balls.

    This means that the golf ball is possibly going to be the one that bounces the highest and the most efficient, the tennis ball will bounce the second highest and the second most efficient, and the field hockey ball will bounce the third highest and the least efficient. Materials: * * golf ball * tennis ball * field hockey ball * a flat surface * 2 meter sticks * tape * electronic balance Procedures: 1. Mass each of the spheres using the electronic balance and record the mass 2.

    • Word count: 676
  24. Physics Case Study

    This is in scale with the ramp in a way that matches a car going down a road. I also tried different balls to make sure that the marble would give me the most reliable results.

    • Word count: 425
  25. How does the Kinetic Energy of a trolley (toy car) depend on the height from which it is released

    Preliminary Work During my preliminary work I tested the lowest and highest heights from which I , I did this to find the shortest and longest times it would take to do the experiment. The results obtained are shown below: Distance from which released (cm) Height from which released (cm) Time 1 (s)

    • Word count: 569

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