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Welcome! Here are the details for experiment
Category : Mechanics By : Phys Uncle  
Experiment's Objective: To determine resultant of two vectors Graphically by (Gravesand’s apparatus)
With the help of this experiment, we can determine the resultant of two forces, acting on an object at different angles.
Gravesand’s apparatus, A4 paper, mirror strip, thread, slotted weights with three hangers, Geometry box
  • Check the pulleys fixed on the board for no friction by revolving them. If they do not rotate smoothly oil them.
  • Set the Gravesand’s apparatus in vertical position on a table with the help of plumb line.
  • Fix a sheet of white paper on the board with help of drawing pins.
  • Take two pieces of thread equal in length to the height of the apparatus and a third piece of thread equal to the length (smaller in length than other threads) of apparatus.
  • Knot them together tightly at one end and tie three hangers at the three free ends.
  • Pass the longer threads over the grooves of the pulleys, and let the third thread along with the hanger remains suspended over board.
  • Load the hangers tied to the longer threads with the suitable slotted weight. Load the third hanger with the slotted weight such that the total weight of the hanger is less then the sum of weight, of the hangers. But this weight should be greater than the total weight of each of the other hangers.
  • Place a mirror strip breadth wise on the paper under one of the threads.
  • Close one eye and look at the image of the thread. Adjust your eye to the position perpendicular to the strip and thread. Get the position when the image gets exactly behind the thread and is hidden under the thread.
  • At this position of your eye mark two points on the paper, each on the either side of the strip exactly beneath the thread.
  • Similarly mark two points for each of the remaining threads.
  • Remove the threads along with the hangers from the pulleys.
  • Join the points and draw three straight lines which will meet at a point O.
  • Note total weight of each hanger, that is, sum of the weight of the hanger add slotted weight on the hanger.
  • Let these weights of the hangers be P, Q and R as shown in the fig.

Figure will be uploaded very soon

  • Select a suitable scale.
  • Cut lines OA, OB and OC to represents the force, P, Q and R respectivelyaccording to the scale.
  • Put the arrow heads at points A, B and C, that is, at the end of OA, OB and OC.
  • From A draw a line  parallel to OB and cut its length AD equal to OB to represent force Q or complete parallelogram OADB.
  • Join OD which is resultant of forces P and Q. denote it by R’.
  • Measure length OD and convert it into gm.wt by the scale selected.
  • Find difference of R and R’.
  • Repeat the experiment by adding weight on each hanger.

The pulleys should be frictionless. The board should be vertical. Load hangers with the heavy weights. Thread must be weightless, thin and strong.

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