• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
  1. 1
  2. 2
  3. 3
  4. 4
  5. 5
  6. 6
  7. 7
  8. 8
  9. 9

In this project I am going to investigate the factors which affect how a bridge bends, and how its sag varies because of the input factors.

Extracts from this document...




        In this project I am going to investigate the factors which affect how a bridge bends, and how its sag varies because of the input factors.

        In general, sags can vary because of a series of input factors, such as the difference in mass, i.e. the load, applying on the bridge, also the difference of its position; the material the bridge made of, in terms of the differences of density; the type the bridge has been designed, such as an arch bridge and a beam bridge are only being supported at two points; a cantilever bridge is being supported by three or more points. The length, width and the thickness of the bridge (i.e. difference in volume).

        The bridge bends under a mass, which can be a static force, less likely to break the bridge, or a dynamic force, more likely to break a bridge. The sag depends the compression (Fig. 1) and, the tension being made to the bonds between atoms of the bridge material.







Fig. 1 A force being exterted onto a bridge


        This investigation focuses on only: -

  1. how sag changes when mass varies when distance between load and pivot is constant;
...read more.


Graphically, I predict that the sag increased constantly would be directly-proportional to the increase of mass, i.e. a straight slope on the graph heading to the top right-hand corner, until it reaches its elastic limit (the yield point).

Varying distance

The sag of a bridge also affected by the change in length. The length is the distance between one of the two pivots and the load in the middle, which means there are two sets of identical rotations, one is clockwise and one is anti-clockwise, are taking place at the same time, this is because of moments.




Fig. 3 The motions when a sag occurs

The moment of force or the turning effect depends on both the size of force and how far it is applied from the fulcrum. It is measured by multiplying the force by the perpendicular distance from the pivot, i.e. Moment = F × d.

        Ignoring one of the two identical turning effects, we are going to investigate how sag is affected by the distance from the pivot to the load.






Fig. 4 The moment acting on the left half of a bending bridge

        As Moment = F × d

...read more.


        I predicted that Sαm, sag of a bridge is directly proportional to the mass applied on it, which this idea was taken from Hooke’s Law focusing on the extension of a spring, is directly proportional to the stretching force. After doing the “varying mass” experiment, I found that Sαm. I predicted correctly.

        I also predicted that sag is the moment, multiplying force and distance; as

I predict that sag, which is the moment (= F × d) of the turning effect would vary proportionally when distance varies. Same for the sag of a bridge, which would vary proportionally as distance varies. After doing the “varying distance experiment, I discovered that my prediction is only partly correct. Sag is not directly proportional to distance, in fact, sag is directly proportional to distance3, Sαd3.


This investigation of the sag of a bridge has been done smoothly. Inaccuracy of results could be made by many factors. It was difficult to make an accurate point M (the middle point) and keep both sides absolutely identical to each other. It was in fact impossible to sellotape the needle and apply a mass at the same point, M. Therefore, measurements could not be read accurately and formed errors.


...read more.

This student written piece of work is one of many that can be found in our GCSE Forces and Motion section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related GCSE Forces and Motion essays

  1. Marked by a teacher

    Investigating a Cantilever.

    4 star(s)

    845 3. 845 1. 824 2. 824 3. 824 1. 21 2. 21 3. 21 21.0 50 500 1. 845 2. 844 3. 844 1. 818 2. 819 3. 819 1. 27 2. 25 3. 25 25.6 Analysis The graph shows that the deflection of a cantilever is directly proportional to the mass that supports it.

  2. Marked by a teacher

    To investigate the factors that affect the stopping distance of a catapulted margarine tub. ...

    4 star(s)

    The car was catapulted, similar to the way that I will catapult my margarine tub in this experiment, so I had to stretch the elastic the same amount every time in order to ensure that that the trolley had the same amount of EPE every time.

  1. In this experiment I aim to find out how the force and mass affect ...

    The force of gravity on earth is always equal to the weight of the object as found by the equation: Fgrav = m * g where g = 9.8 m/s2 (on Earth) and m = mass (in kg) Normal Force, Fnorm The normal force is the support force exerted upon an object which is in contact with another stable object.

  2. Physics Coursework: To investigate the Oscillations of a mass on a spring

    A single motion from one extreme position to the other and back, passing through the neutral position twice, is called a cycle. The number of cycles per second, or hertz (Hz), is known as the frequency of the oscillation. To find out the frequency, this formula can be used: A

  1. This investigation will be looking at what factors affect the performance of a squash ...

    175 30 200 32 Having evaluated the results, I believed that a fixed height of one metre would be appropriate with the resultant heights covering a greater range than if a fixed height of say 50cm was used. On the other hand, if I dropped the ball from 2 metres

  2. My objective in this experiment is to find out how a spring varies in ...

    Since the strain is proportional to the stress for different materials where Hooke's Law is true, then there should be a fixed ratio of stress to strain for a given elastic material. This ratio is known as its Young's Modulus.

  1. Physics investigation into the bending of a Cantilever.

    the force stretching it and therefore if the length doubles the force must double also. This theory has been applied to the cantilever and therefore the deflection such as a spring is proportional to the deflecting force such as a force that would be stretching the spring.

  2. Controlled Assesment Experiment - The extension of a rubber band depends on the force ...

    * For an object that is able to recover its original shape, elastic potential energy is stored in the object when work is done on the object to change its shape. * The extension of an elastic object is directly proportional to the force applied, provided that the limit of

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work