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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.
To keep the experiment as fair as possible, I will only change one variable at a time. Each experiment will be repeated three times and an average result will be calculated to obtain more accurate data. For the first part of the experiment I will only vary the height, by clamping the inclined plane higher. I will release the dynamic trolley at the same point each time on the inclined plane. The same trolley will be used for each experiment so that the mass is kept constant and therefore is not a variable.
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Investigate the various ways in which physics is involved to create exhilarating rides in theme parks.
Two triangles are similar if they have the same shape. They don't have to be the same size. For the smaller triangle, I will evaluate the ratio of the side with length h to the side with length l. This is the same as, with respect to the larger triangle, the ratio of the side with length H to the side with length L. That is h/l = H/L I used two rulers to record the measurements of l and h, the two rulers being 90 degrees parallel to one another. The value of L, length, was recorded by the distance from where I was to the point at where the ride is situated.
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Regarding the volume, I believe that the volume will increase exponentially up to 100� c. Preliminary testing: Before I and to conduct the investigation, I carried out some preliminary testing, to ensure that the investigation I had choose was valid and was going to provide me with some sound results. I began by deciding what I was going to measure and test, and what my variables were going to be. I decided that I was only going to have one variable, temperature, which is mentioned in more detail below, and 4 tests, each one related to the elasticity of the squash ball and each one conducted at that temperature.
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I looked at a clock with a pendulum to see how it worked. I found that to change the speed of a second you adjust the length of the pole which the pendulum hangs from, so I also based my prediction on that as it is the same principle. I set up a trial experiment to test out the following: * Which angle of displacement to use (e.g. 90�) * How many readings to take * Which lengths of string to measure (e.g. every 10cm) * Where to carry out the experiment (on a desk/floor etc..)
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The weight of the Marble will affect the distance it roll and also the speed at which it rolls at. This is because the heavier an object is the more gravitation potential energy it could have if it was lifted. The size of the marble may also be proportional to the weight, it will also cause more friction because there will be more surface area of the ramp touching the marble, this will slow it down and decrease its rolling distance.
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Investigating Sliding Friction: the effect of weight on sliding friction between a block and surface.
This formula shows that the force of friction is proportional to the original force/ weight of the object. The formula is the work of Leonardo da Vinci. He said "Friction produces double the amount of effort if the weight is doubled." This should be because if the force on an object is increased then the forced needed to move it would also have to increase. In this experiment I will make sure that I keep everything the same except the weight of the block, as the weight is my variable. The things that I must keep the same are: > Surface the block is sliding on > The wooden block- because the grain of the wood would change and also the initial starting weight would be different.
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An Investigation To Find Out What Effect The Weight Of A Falling Object Has On The Terminal Velocity Of It.
The preliminary work that I did helped me to plan my actual investigation better, as I learnt from the mistakes that I made. These were things like starting the stopwatch slightly late or early, which changed the times of my results. I also learnt that one metre was not high enough as it did not give me enough time to start and stop the clock accurately. I am glad that I did a preliminary experiment, as now, when I do my actual experiment I will feel more confident using the apparatus.
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The bigger the force on an object the greater the work done. Energy Elastic Potential Energy = stored in an elastic object when work is done on the object to change its shape. Kinetic Energy = the energy an object has because of its movement. An object has more kinetic energy the greater its mass and speed. Prediction I predict that as the weight in the margarine tub is increased the distance it will travel is decreased. I think that the elastic potential energy will also decrease as the weight increases.
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Terminal Velocity - Maximum velocity which a freely falling object reaches when it is falling through a viscous (semi-fluid) medium such as air. If the effects of the medium through which a body is falling towards the Earth were ignored, the body would, theoretically, continue to accelerate until it hit the ground. In practice, the viscous nature of the medium creates a force acting against the motion, which tends to reduce the acceleration of the body. This force is only small when the object is moving slowly, but gets larger as the velocity of the object increases until, eventually, it equals the accelerating force (the weight of the object), so that there is no further acceleration.
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Exp 1 Changing Length (variable) Mass = 80g Angle = 5o LENGTH (IN METRES) TIME (IN SECONDS) (FOR 10 SWINGS) TIME (IN SECONDS) (FOR 1 SWING) L1 - 0.5 = 16.46 secs 1.65 L2 - 0.4 = 13.98 secs 1.40 L3 - 0.3 = 12.42 1.24 L4 - 0.2 = 10.91 1.09 L5 - 0.1 = 8.71 0.87 These results show me that the length of the string does affect the time for the pendulum to swing. Experiment 2 I will investigate the relationship between the weight of the pendulum, and the time it takes for the pendulum to make 1 full swing. > Hypothesis: I don't think the weight will affect the time.
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Hence, my Independent Variable will be the vertical height that I drop my parachute from. I will also keep the parachute the same - not change the length of the string or the measurements of the bin liner. I am going to measure the time taken for the parachute to reach the ground from the desired height. Other variables that could be investigated are: The Surface area of the parachute, The Length of string (between the parachute and mass), which might control the volume of air under the parachute. A Distribution of mass, i.e. perhaps on the parachute itself as opposed to on string attached to the parachute (this of course would not be a continuous variable so it would not be of great value).
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I have worked out using the sine function (Trigonometry) that the start of the ramp needs to be 68.83 (2 d.p.) off the ground. The toy car will be released from the top of the ramp and will roll down. The toy car will be rolled down once. When rolled, the final velocity of the toy car as it rolls down the ramp will be measured. This will be measured by a human stopping the stop watch when the car passed a certain point near to the end of the ramp.
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Acceleration is a rate of change in velocity. It is the rate at which an object's speed is increasing or decreasing. To work out the velocity of an object we need to know the change in velocity and the time taken for the change in velocity. Acceleration is measured in metres per second squared ( m/s�). During my experiment there will be certain forces acting on the car, When the car is stationary there is a downward force exerted by the weight of the object and an upwards force exerted by the surface.
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* Surface Bounced on Difficult to measure so lab floor will be used constantly. * Height Dropped from 1 metre * Material Material of ball is made of a particular type of mass as given by the world governing bodies Method Heat ball up then place it in a beaker of boiling water. Then measure the temperature and drop the ball in at 1m. Measure temperature of water to find out the temperature of squash ball. To get the ball at an accurate temperature the entire ball must be submerged.
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Diagram: Safety: In an experiment like this there aren't many safety precautions to take as nothing dangerous is being used but the ramps could easily be tripped over and cause injuries - to ensure this doesn't happen people must act sensibly. Method: * Set up the apparatus as it is show in the diagram * Make sure the ramp is marked at every 10cm from the bottom of the ramp * Start the toy car from behind the 10cm mark on the ramp, let it roll down the ramp and measure the distance it travels with the rulers.
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Mass - the heavier the ball is the faster it will fall due to the gravitational pull of the earth meaning it has weight as well. Prediction. I predict that the higher the ball is dropped from the higher it will bounce because the ball will gain more kinetic energy on the way down because potential energy equals to mass multiplied by gravity multiplied by height (PE=mgh) and height is the easiest factor to change out of the three. Method.
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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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Diagram: Factors that affect terminal velocity: The accelerating force acting on all falling objects is gravity, and if it wasn't for air resistance everything would fall at the same rate, (as on the moon). However due to air resistance, things fall at different speeds for a number of reasons. The drag of an object (its shape and area), in comparison to is weight, is what alters terminal velocity. Therefore we can determine that three things that can affect the terminal velocity of an object are its shape, its area, and its weight.
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A pendulum will oscillate with simple harmonic motion provided that the amplitude is small. Amplitude is the maximum displacement from the centre of oscillation. The time period of a pendulum can be found using the equation: T = 2? L g * T = Time taken for one complete oscillation (s). * L = Length of the pendulum string (m). * g = Acceleration due to gravity (ms��). The above equation shows that the period of a simple pendulum depends on two factors: * The length of the pendulum i.e Time period VLength Or (Time period)� Length. * Acceleration due to gravity i.e the position of the pendulum from the centre of the earth.
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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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We chose to keep the weight at 500g and the angle kept at 45�. For the changing of the angle we chose to keep the length of the string at 30cm and the weight at 500g. Finally for the changing of the weight we chose to keep the length of string at 30cm and angle at 45�. We must make sure that when we time the period that we do so by marking the swings from the centre of its swing, and that one period is equal to the pendulum bob having passed the central point twice as demonstrated in the diagram below.
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making the experiment inaccurate > All I have to change is the height of the of the ramp from the ground it's resting on. And by keeping the length of the ramp constant that would in turn proportionally change the angle of the ramp. If I managed to keep all the factors that I need constant, constant and would provide expected results then my experiment would be a fair and accurate test. Preliminary Work Golf Ball Height of Slope Angle of slope Time Taken (s)
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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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