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GCSE: Forces and Motion
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Balanced and unbalanced forces
- 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 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 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 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 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 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 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.
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 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 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 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 What is the weight of a mass of 20 kg? W = mg = 20 x 9.81 = 196.2 N
- 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 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 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
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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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.
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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.
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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
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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.
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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)
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In this experiment we are focusing on a particular type of potential energy, gravitational energy. (From here on, the phase potential energy will be referred to as gravitational potential energy.) Potential energy is the energy stored in an object as a result of its vertical position (i.e., height.) The energy is stored as the result of the gravitational attraction of the earth for the object. There is a direct relationship between the potential energy, the mass of the object and also the height of the object. In this case we are using the same trolley so therefore the mass is the same, but we are changing the gradient of the ramp and by changing the gradient we are also changing the height.
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This is because the weight is great than the drag force, causing there to be an unbalanced force. The force necessary to accelerate an object by a given amount depends on the object's mass, therefore the greater the mass, the greater the force must be. Chosen Variable I have decided choosing the total surface area of the wingspan in my investigation and the reasoning behind this decision is that I believe this variable from my preliminary work would be much better to collect results from for my analysis. When executing my preliminary tests prior to this investigation, I noticed that when dropping my helicopter with an altered mass, the vertical acceleration time did not seem to have considerable differences between the starting and finishing points as it did for the wingspan.
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When applying the model to real life it is important to know the Hooke's constant as further predictions and calculations can then be applied to determine other variables such as the appropriate length of the chord, the extension and force. Length, extension and force are extremely crucial because if the person is too heavy the elastic will extend too much, if the person is too light the jump will be jolty and possibly cause injury. Therefore extensive planning and research has to be conducted in order to design an effective model, which could then be applied as the foundation for the Story Bridge bungee jump.
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so that there were in total three, sturdy fins. The rectangular strips were then folded flat, in an outwards direction facing opposite to each other, so that if placed on a flat surface the fins would stand erect. The fins were then glued onto the base of the body of the rocket (which had already been accommodated for by the cardboard tubing of the wrapping paper), an equal distance apart so that when upright, the rocket would be supported by its fins.
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and the ball travels further before stopping. Therefore the ball goes higher. * The higher the ball goes, the more GPE it ends up with. Therefore the ball ends up with more GPE In short: GPE=Mass (kg) � Gravitational Field Strength (N/Kg) � Height (m) If we let mass = m Gravitational Field Strength = g Height = h1 An increase in h1, assuming g and m stay constant, results in an increase in m � g � h1 which results in an increase in GPE. A decrease in h1, assuming g and m stay constant, results in a decrease in m � g � h1 which results in a decrease in GPE.
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When n springs of the same type are used in serial, the value of spring constant is 1/n of the spring constant of one spring. * The efficiency of the spring - The springs keep on converting energy between the forms of elastic potential energy and kinetic energy. But the conversions cannot be 100% efficient, which means some energy is lost in the form of heat energy (by air resistance or friction) or sound. This is the main reason that the oscillation will eventually stop.
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Such problems cannot be fully controlled with the equipment available but steps can be taken to avoid them. This is why the same person reads the height of the bounce, and they stand in exactly the same place for each test. Also the same person releases the ball without any intentional force each time. My hypotheses for this experiment are: > The greater the height a ball is dropped from the greater the height of the bounce. > The greater the elasticity of a ball the higher it will bounce.
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Length: as we can see from the equation the length is one of the effective factors on the period of the pendulum so I measured the thread for different lengths. As the Galileo's formula says mass of pendulum and the angle from which the pendulum is released do not effect the period but I haven't proved them yet so I keep every variable apart from length unchanged and angle I will choose is 10� and the mass of pendulum is 0.05 kg.
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Diagram: Hypothesis: I know that the speed and braking distance vary when the height of the ramp height is altered so I plan to investigate the relationship and I predict that as the height of the ramp increases so will the braking distance and velocity. This is because if the ramp was at 0� to the bench then the forces would be balanced and therefore no movement takes place whereas if it is at a much greater height the balance forces become unbalanced.
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Gravitational field - The ball bearings fall through the glycerol due to the attraction created by the gravitational field from the Earth. In this investigation, this can be considered constant at 9.8ms-2. Friction - Whilst friction created by the viscosity of the fluid has already been discussed, friction due to the sides of the tube may also play a part if the vertical tube is narrow. To minimize this, in the investigation, ball bearings were dropped from the centre of the tube so that they were less likely to experience friction due to the sides of the tube.
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A more successful and accurate method however, uses a sound sensitive instrument/ device connected to a picoscope programme on the laptop called Dr Daq. This is very sensitive to sound, and so as the ball bounces it measures the time difference between each bounce. This is possible due to the sound produced by the ball as it hits the table, because each time a ball bounces it loses some of it's energy in the form of sound. The Dr Daq picks up the sound produced by the ball and produces a voltage which is picked up by the picoscope programme, producing a voltage against time graph.
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This ratio may be graphically shown by means of a diagram with the stress on the y-axis and the strain on the x-axis. This is known as the stress-strain diagram. Within the limit mentioned above the diagram is a straight line. The greater the resistance a material offers to deformation the steeper the vertical axis will be the line. If the results of similar experiments on different materials of a meter rule are plotted to the same scales, comparison is easy.
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Similarly the force needed to change the velocity (acceleration) of a moving object will depend upon it mass. The stronger the force applied the more will the acceleration be. The more the mass of an object, the less will the acceleration of the object when the same amount of force is applied. So one can express that acceleration (a) is directly proportional to the Force (F) applied to an object and inversely proportional to the mass (m) of the object.
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both proportional to each other then I can form the equation 1/2 x m x Va� 1/2 x m x Vr� If I divide both sides by (1/2 x m) then I'm left with Va� Vr� and by doing the square root of both sides then I'm left with Va Vr. This shows that the relationship between them both must be proportional. In my experiment I intend on proving this relationship in the form of results. As the ball travels down the slope then some of the potential energy is gradually changed into kinetic energy, which causes the ball to gain momentum.
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The cardboard bridges keep the wire straight and in place throughout its length. The pulley allows the wire to move freely along it to keep friction low. As the load increases on the string, the string goes under tensile strain and may extend in length, this is the variable I will be measuring. A micrometer has been used to measure the diameter of each of the three different manila wires. Each string was cut to 650mm, using a metre rule.
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In fact, my calculation should consider the rotational energy of the object. However, this will make the calculation very complicated and it is beyond our syllabus, so the rotational energy has been ignored. To minimise this error, I need to be careful that do not use something will round along the slope or has strange shape. To simplify this experiment, air resistance has been ignored as a factor in the range of the projectile. As it is a projectile(after leave the wood ramp) that will be measured, the only other factor working on it are gravitational forces.
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The variation in temperature affects the viscosity of a fluid. Increasing the temperature lowers the viscosity of the fluid. The fluid becomes thinner, less viscous and flows more freely. This is because molecules gain energy when the temperature is increased, so that they are moving at a high velocity and collide more successfully. However, when the fluid becomes cooler the viscosity increases and as the fluid becomes thicker, the rate of velocity becomes lower and doesn't flow as easily. This is due to the reduction in energy from the molecules, which in turn reduces the movement of molecules.
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It is measured in metres-per-second per second (m/s/s) or meters-per-second squared (m/s�), and it tells you how much the velocity will change each second. The acceleration of an object can be calculated by using the following formula: (average) acceleration (m/s�) = change in velocity (m/s) or in symbols: a = v - u time taken for the change (s) t where u is the velocity at the beginning of the time interval and v is the velocity at the end of the time interval. When an object is slowing down the change in the velocity is negative (because v is less than u), and so the acceleration is negative.
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How does the temperature of a squash ball affects the impact time of the ball drops from a certain height.
5 Ways of measuring impact time 5 Final decision and the experimental set up 10 Experiment (b) 12 Results and Analysis Data collection 13 Analysis 18 Discussion 21 Evaluation of the Experiment Evaluation 22 Improvement 23 Conclusion 24 Appendix 25 References Bibliography Introduction Squash has become more and more popular nowadays. Moreover there is a growing trend of keeping a healthy life in the modern society. Squash is one of the most energy consuming sports. It just fits the people's want, as time is precious in the city. For the reason of being an enthusiastic player in squash, I investigated this sport in the field of physics.
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