Stretching Springs/Hookes Law.
Stretching Springs/Hookes Law
A force is able to change the shape of an object, the more the strength and force you apply, the more the shape of the object will change because the particles of the object are being moved therefore it will change the shape of the object because of the particles being pushed for e.g.
A force is also able to change the motion of the object.
The force, which is applied to the object, makes the object stay in that shape which is the cause of the force hitting the object and making it change, this will not go back to its original shape like shown in number 2, this is because the particles have been hit so hard that the attraction of the particles which makes them go back to its original shape have been damaged so it will then go into another shape.
This is a material that will stretch and go back to normal, its original shape.
Elastics behavior is the ability of a solid to regain its shape when the external forces are removed.
What is Hookes Law?
Hokes Law is a rule for a spring,
‘For a spring-that for a helical spring or other elastic material the extension is directly proportional to the applied force provided the elastic limit is not exceeded’
This means that the extension is directly proportional to its force until its elastic limit.
The graph or load against extension is a straight line. When the load is doubled, the extension doubles, this relationship is known as one of direct proportional.
This result is in agreement with Hookes Law. This law is named after Robert Hooke who first the relationship between the amounts of stretch in objects compared to the load force acting on the object.
This graph shows the increase in length of an elastic wire as the stretching force on it increases. Over the straight-line part of the graph there is a 10-mm increase in length for every extra Newton (N) of applied force. The change in length (strain) is proportional to the force (stress), a relationship called Hooke’s law. The wire begins to stretch disproportionately beyond an applied force of 8 N, which is the wire’s elastic limit. When this force is removed, although the wire will decrease in length somewhat, it will not go back to its original length.
What happens to a spring when forces are added to it?
When a string is stretched and then released it returns to its original shape and length, however this is only in use if the spring isn’t overstretched.
An overstretched is noticeable and can’t be returned to its original position because the coil pulls out and it changes the shape of the coil and so can’t return to normal when the force is taken off due to the attraction particles being pulled apart.
As the force increases the spring increases until it has a point where it goes past its elastic limit.
When we put weight on the spring it expands due to the particles being pulled and then expanding.
When we apply a force the spring expands, the spring works by forces of attraction between the particles.
Patterns we expect to see
The patterns we expect to see are as the weight increases the length of the spring should increase because the particles are being stretched more and more so the spring will go bigger and bigger.
Elastic limit of a spring
The elastic limit is a point which the spring becomes deformed and at a point where the amount of stretch is no longer directly proportional to the load. The spring will be deformed and will no longer return to its original length.
This is because the particles have been stretched too much and can’t stretch any more because the attraction between the particles have been damaged due to the overstretching, therefore this will then not return to its original place. Also the external force applied to a material creates stress within the material; this stress causes the material to deform.
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Elasticity (physics ), property of a material that causes it to resume its original size and shape after having been compressed or stretched by an external force. An external force applied to a material creates stress within the material; this stress causes the material to deform. The amount of deformation, as a fraction of the original size, is called strain. For many materials, including metals and minerals, stress is directly proportional to strain over a certain range of these quantities. This relationship is known as Hooke’s Law after the British physicist Robert Hooke, who first expressed it. However, if the external force is too strong, the material can become permanently deformed, and Hooke’s Law no longer applies. The maximum amount of stress a material can withstand before becoming permanently deformed is called the elastic limit.
The ratio of stress to strain, called the elastic modulus, and the elastic limit of a material are determined by the molecular structure of the material. The distance between molecules in a stress-free material depends on a balance between the molecular forces of attraction and repulsion. When an external force is applied, creating stress within the material, the molecular distances change and the material becomes deformed. If the molecules are tightly bound to each other, there will be little strain even for a large amount of stress. If, however, the molecules are loosely bonded to each other, a relatively small amount of stress will cause a large amount of strain. Below the elastic limit, when the applied force is removed, the molecules return to their balanced position, and the elastic material goes back to its original shape. Beyond the elastic limit, the applied force separates the molecules to such an extent that they are unable to return to their original positions, and the material is permanently deformed or broken apart.
From Encarta 99
The 2 opposite forces on the spring
The 2 opposite forces are-:
- The pull in the spring, which supports the mass, is a tension.
- The force that the object exerts on the spring is called the load.
There is also gravity acting on the spring.
Robert Hooke was an English scientist and was best known for his study of elasticity. He made a law about elasticity, which was named after him and was called Hookes Law.
Hooke, Robert (1635-1703), English scientist, best known for his study of elasticity. Hooke also made original contributions to many other fields of science.
Hooke was born on the Isle of Wight and educated at the University of Oxford. He served as assistant to the physicist Robert Boyle, and helped Boyle in the construction of the air pump. In 1662 Hooke was appointed curator of experiments of the Royal Society and served in this position until his death. He was elected a Fellow of the Royal Society in 1663 and was appointed Gresham Professor of Geometry at the University of Oxford in 1665. After the Great Fire of London in 1666, he was appointed surveyor of London, and he designed many buildings, including Montague House and Bethlehem Hospital.
Hooke anticipated some of the most important discoveries and inventions of his time but failed to carry many of them through to completion. He formulated the theory of planetary motion as a problem in mechanics, and grasped, but did not develop mathematically, the fundamental theory on which Sir Isaac Newton formulated the law of gravitation. Hooke's most important contributions include the correct formulation of the theory of elasticity, which states that an elastic body stretches in proportion to the force that acts upon it; and analysis of the nature of combustion. He was the first to use the balance spring for the regulation of watches, and he devised improvements in pendulum clocks. Hooke also pioneered in microscopic research and published his observations, which included the discovery of plant cells.
The aim of this investigation is to find out if extension is proportional to the force applied, and to find out the elastic limit of our spring which we will measure each time a different weight is put on, also to find out the length of the spring each time a different weight is put on.
The extension of the spring will be used to judge the strength of the spring. We will measure accurately by measuring if in a fair way and to the nearest mm to get good and accurate results. This will be important because this will show us our results and if the results are not accurate then our whole experiment will turn out to be wrong.
The variable I will be looking at is changing the force applied by changing the number of neutrons we are putting on the spring.
I will measure the spring before putting the weights on and after the weights have been put on how much it has stretched since the last weight, I will also measure the spring from the same point so that it is fair test because if I don’t then my results won’t be accurate and it won’t be a fair test. The important thing about measuring the stretched spring is, if I measure accurately then it will be good, if I don’t my results will be wrong therefore my graph and whatever I use from the graph will be wrong.
I will measure the spring not the 2 rings at the top of the spring to get good result; this is what I did on my experiment. I will also measure in mm to get better accuracy.
The amount of forces I will add is 100g which is 1N each time, this is also to make it a fair test because if you use 100g, 200g, 300g or 1N, 2N, 3N it will be appropriate and it will produce good information with a good variety but if you use 1N then 10N it wont be a fair test because you are jumping too much and it will not give you good results because there isn’t a wide range to use. The size of the force I will use is I will use gentle force to put the weights on because this will prevent damage to the spring because if I put a lot of force on then I might damage the spring and it wont be a fair test, and it will keep swinging and it also wont make it fair test because this might cause stress to the spring which will change the reaction of the spring which will change the results I get.
I also made sure that I measured the spring at the beginning to find out what its original length was so that I can use it in my calculations to find out an average. I also measured at eye level so that I would get good accurate result s so that it would be a fair test.
The spring that we will use will be kept the same to make it fair test, because if we changed the spring we wouldn’t know what the exact extension was and we wouldn’t get our best results and it will not be a fair test. And we will also keep the spring same type of spring to make it a fair test.
We will take the measurements as soon as we have added the weights because if we don’t then the weight will stay on the spring for long and it might change the length of the spring, which will affect our results, and we wont get good and accurate results and also it wont be fair test.
It is also important not to just drop the force on the spring but lower the force gently on the hook because this will make if a fair test because if we put the weights on just like that it will start swinging and it will damage the spring therefore it wont be a fair test because we wont be able to measure it properly while it is swinging, this could also change the stress of the spring and change our whole results which would not be a fair test.
We will repeat the experiment and do it twice to make it a fairer test and to get an average.
To make this a safe experiment I will wear goggles to protect my eyes from anything that might fly up like a spring. We will also try to keep the table clean to make it safe and we will also remove all bags or put them under the table or hang them up just in case so no one falls over. We will also remove all stools so that no one will fall over and we will put them under the tables.
Each time the amount of force applied changes the length of the spring will double each time the Newton has been doubled, it should double the amount of force to the elastic limit.
This will happen because the amount of bonds will be stretched therefore it will make the particles move and change places.
The forces of attraction/bonds between the particles stretches because when it stretches it makes the particles separate, so it then after the weights have been removed go back to normal because they are attracted to each other only if the weights that are put on do not make the spring go past its elastic limit because if they do they will not attract and go back to its original position because they have been damaged.
There are forces acting on a spring, which one of them is downwards because the spring is being pulled upwards and as it bounces back up it is being pulled downwards.
Hookes Law will be shown because hookes says that the spring can only take a certain amount of weights before it goes past its elastic limit and I think this is what’ll happen because 2N should stretch so much and 4N should stretch so much until its elastic limit. I will know Hooke’s law will be obeyed because if it isn’t then it will go past its elastic limit like Robert Hooke says.
I think that the graph will be proportional to the force applied until it starts going all anomalous.
The elastic limit is a point until which a point when the spring becomes deformed.
I think that I might reach the elastic limit because I think I will make the spring deformed by putting on more weight than it can take. I will know when the spring becomes deformed when the spring starts going longer and longer (the extension) until it completely becomes deformed. The spring will become too big and it’ll not be able to take any more weights once it is past its elastic limit. The particles causes the elastic limit because of the bonds, because they don’t attract so they don’t go back to normal so the spring becomes deformed. I predict to see proportional results until it goes past its elastic limit.
-The first thing I will do is go and collect all the equipment and all the safety equipment-:
-I will then set up all the equipment
-I will then put on the spring carefully so that I don’t damage the spring to make it a fair test.
-I will then put the weights on the spring and to make it a fair test and I will make sure I put the weights on slowly so I don’t damage the spring and I will make sure I put the weights on when the spring isn’t swinging because it might damage the spring and it wont be a fair test.
-I will then measure the spring in mm.
-I will them take the weights off and measure the extension in mm, I will take it off slowly so I don’t make the spring swing because it will add stress which will not be a fair test
-I will measure at the bottom of the spring each time at the same point to make it a fair test.
-I will then add the next mass and put it on carefully when it isn’t swinging to make it a fair test and to avoid stress because it wont be a fair test, I will add 1N at a time also to make it a fair test because 1n-5N is jumping too much so it wont be a fair test, I will do this for every mass.
I will then repeat the experiment and do it twice to find an average.
To extend this investigation I could look at different springs of different materials or use a different wire of different thickness.
My results show that the force is proportional to its extension until it reaches its elastic limit, which was 10N and this shows that it has obeyed Hookes Law. My results also show that as you add more weights the length of the spring goes bigger. The line on my graph shows that the force is proportional to the extension throughout the graph until it reaches a certain graph where it goes past its elastic limit where there is a curve, this shows the elastic limit which is at the 10N position, it also tells me that the Newton’s added should be in proportional with the length of the spring.
My results tell me that my prediction was correct because I said if the Newton’s increased the length of the spring should increase and this is what happened as I can tell from my graph for e.g. 1N=40mm and as we go up 2N= 70mm so it does go up. The thing that happen was as the Newton’s increase the length of the spring increases because I said 0.5N=10mm and 1N=20mm in reality it was 0.5N=4omm and 1N=65.
My quantative prediction was incorrect because I said if the Newton’s doubled the length should double, this was because it isn’t what happened,
but in reality it was
So it isn’t quite doubled so I am wrong with my quantative prediction.
My prediction was right because I said that as the Newton’s go up the length should go up because of the bonds, they are pulled apart so they extend as they are pulled apart more when more weigh is added because they are being pulled apart more so they extend more, this is exactly what happened so I was right.
I found the elastic limit because it showed on my graph, it shows the force is proportional to the extension until there is a curve, this is the elastic limit, this is where I thought the elastic limit was, where the curve was I found this out because the results don’t follow the pattern because 6N=300mm and 12N=600mm but in reality it was 6N=300 and 12N=650mm, I t took 11N for it to reach its elastic limit.
The graph tells me that increasing the force should affect the extension of the spring by the extension going up as the force goes up as it shows on my graph and this is exactly what happen-:
The graph shows that its force is proportional to the extension and my graph shows this where the force is in direct force with the extension and this law obeys Hookes Law.
In my investigation I had a couple of anomalous results because I can tell my graph because they don’t follow the pattern and they don’t match the line of best fit this might be because of measurement errors.
The following are likely to cause errors in my experiment and I could prevent them by-:
-I could measure the length of the spring wrong, to overcome this by using a measuring tape as it is better and easier to get closer and measure, I could also read at eye level to overcome this.
-I could use accurate use of weights with a broad range like 1, 2, 3, 4, 5, Newton’s.
-I could measure wrong and I could prevent this by measuring closer because it’ll be easier to read off, and it’ll be better if I read off eye level because it will be better and it will be a fair test.
-Forces could be applied for more than a constant time so I could prevent this by applying the weights for a constant time.
-I could cause stress on the spring by putting the weights on for too long and I could prevent this by taking the weights off on time so it could prevent it from happening and causing stress.
-I could also cover the spring to stop it swinging and to stop stress, and it’ll also stop draughts, which make the spring, swing, this would make it a fair test.
-I could’ve measured the spring from top and bottom and to prevent this by measuring it from the actual coil.
I would’ve been able to draw my graph more precisely if I had more readings and a wider range, it would’ve been better if I had 3 springs because I would’ve done it 3 times and I would’ve got a better average. I would choose these results with the 3 springs rather than my original ones because it would be better and more accurate with 3 springs.
I used information from Encarta to get information about Robert hooke I also used my science note book and the book science for you.