Write an activity to construct a beam balance.
Answers
Answer:
Beam balance is an apparatus used to measure mass of different objects by comparing it with a known mass. It consists of a horizontal beam with a support at its centre and depends on the gravitational pull on it.
In this TACtivity, we will learn to make a beam balance to measure and compare the mass of different objects using the given weights.
Tools
Paper Cutter
Binding/Metal Wire
Insulation Tape
Scissors
Candle
Parts
Plastic Bottle
× 2
Cotton Thread
× 6
Cycle Spoke
× 2
Spoke Nut
Nuts
× 20
Template
Precautions
Handle the paper cutter/scissors with care.
If using the candle, light it with care under adult supervision.
You need two plastic bottles of the same size.
Take a plastic bottle.
Cut the bottle in half using a paper cutter/scissors.
Repeat the above step for the other bottle.
Only the bottom part of the bottles are needed for this TACtivity.
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Step 2 - Making Holes
Place the cut bottle on the given template, such that the centre of the bottle is placed above the dot of the template. Draw three lines on the bottle, which are perpendicular to the lines on the given template.
Place the cut bottle on the given template, such that the centre of the bottle is placed above the dot of the template. Draw three lines on the bottle, which are perpendicular to the lines on the given template.
Measure and mark 2 cm, along a line drawn in the previous step, from the top of the cut bottle. Heat a metal wire/spoke on a candle flame and make a hole at the marked point.
Repeat the above step to make holes on the other two lines.
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Step 3 - Connecting Threads
Take 3 pieces of thread of equal length (~25cm). Insert each piece of thread into each of the three holes and secure them with knots on the bottle.
Take 3 pieces of thread of equal length (~25cm). Insert each piece of thread into each of the three holes and secure them with knots on the bottle.
Repeat the above steps for the other cut bottle.
The two bottles will now act as weight holders.
Tie all the three threads together with a knot at the loose ends.
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Step 4 - Preparing the "Beam"
Join the two spokes by screwing the spoke nut halfway into the threaded end of each spoke. Now, this acts as the beam.
Join the two spokes by screwing the spoke nut halfway into the threaded end of each spoke. Now, this acts as the beam.
Balance the beam on two fingers to find out the centre of gravity of the beam. Identify the point at which the beam remains horizontal, when balanced on your fingers. Once you find the approximate point, identified as the centre of gravity, try balancing the beam at the identified point on one finger only.
Tie a 10 cm thread at the point, identified as the centre of gravity, on the spoke assembly.
Use insulation tape near the thread, to secure it firmly at the desired position.
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Step 5 - Balancing the Beam
Place the weight holders at the extreme ends of the "beam" and use insulation tape to secure them.
Place the weight holders at the extreme ends of the "beam" and use insulation tape to secure them.
Try to balance the two weight holders.
If the beam is not balanced with empty bottles as seen in the picture, use layers of insulation tape at the extreme ends of the spoke as counter weights to balance the beam.
A balanced beam gives an accurate result.
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Step 6 - Balanced Beam
The balanced beam can be seen in this picture.
The balanced beam can be seen in this picture.
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Play - Balancing Weights
Play with your beam balance using the given nuts. Add different number of nuts on either side of the weight holder and observe.
Play with your beam balance using the given nuts. Add different number of nuts on either side of the weight holder and observe.
1 nut weighs 1 g each. Use the nuts to weigh various objects.
For example, place a stone on one side of the balance and continue to add nuts to the other side, until the weight holders are at the same horizontal level. Count the number of nuts in the weight holder and record it, which will be the mass of the stone. Verify the mass by weighing it on a weighing scale.
Answer:
Beam balance is an apparatus used to measure mass of different objects by comparing it with a known mass. It consists of a horizontal beam with a support at its centre and depends on the gravitational pull on it.
Apparatus and Materials
For each student group
Beam with regular markings, simple
Wooden prism block
Metal loads, square and identical
Health & Safety and Technical Notes
Read our standard health & safety guidance
These items of apparatus are available from educational suppliers as part of a "lever kit".
The square metal loads should have approximately the same diagonal length as the width of the beam.
Procedure
Place the wooden prism block underneath the centre of the wooden beam. The block acts as a pivot.
Rest a paper clip on the beam and move it closer to or further from the pivot to balance the beam as well as you can. You won't be able to get the beam to balance exactly. When it is very close to being balanced then it tips one way as easily as the other. Fix the paper clip under the beam with a little Sellotape.
Place one square load, 1 unit of length along the beam from the pivot, placing the diagonal of the square along the line of the first distance mark on the beam.
Balance this, roughly, with one square load on the other side of the pivot. Make a written record of the number of square loads and their distances from the pivot.
Add a square load on top of one of the others, to make a pile of two on one side of the pivot. Move the single square load on the other side so that the beam is roughly balanced again. Make a record of the numbers of loads and their distances.
Add another load to make a pile of three. Move the single load again, to roughly balance the beam.
You will find it useful to put your records into a table. A table is easier to make and use than a long list.
Make the pile of square loads four high and five high. Move the single load each time so that the beam is roughly balanced. Record all of your results. There is a pattern in the result. Try to spot it.
OPTIONAL: Put two loads at two positions on one side of the pivot and try to balance them with one load on the other. Repeat a few times, at different distances and try to spot the pattern in these results.
Teaching Notes
The pattern in the results can be described in several ways.
A student who says words to the effect that, 'doubling the load on one side requires the distance on the other side to be doubled' has spotted the pattern. One who says that, 'the product of load and distance is the same on both sides of the beam when it is balanced' has provided a more general description that can be used to make predictions. In other words, the beam balances when the anti-clockwise moment equals the clockwise moment.
Different students will require different amounts of support in this. The most able will not only identify a pattern but will see for themselves that they can use it to make predictions of load position in order to achieve balance. Others will not see a pattern at all unless it is directly pointed out to them. It is worth explaining that the pattern is important because of its predictive power, which can be applied in many practical situations.
Students' application of the predictive power of their new learning can be tested by moving the multiple loads to two marks from the pivot, and asking them to say where the single load must be placed for balance.
The number of loads here provides a measurement of weight, or force.
The product of the force and its distance from the pivot is a measure of its turning effect, and is called the --moment-- of the force.
For balance, the sum of the clockwise moments is the same as the sum of the anticlockwise moments. Large forces on one side of the fulcrum can be balanced by smaller forces on the other, provided that the smaller force is further from the fulcrum.
To illustrate the turning effect of a force, demonstrate with the classroom door. Try pushing it at the edge, then close to the hinge, then at intermediate positions. Compare the effects. You could try pushing near the hinge while a pupil pushes (from the other side) farther out. If you do this then take care that fingers cannot be trapped if the door closes.
An interesting variation is to replace the variable load by a weak spring such as an expendable steel spring.
To do this, place the pivot near the edge of the table. Tie the upper end of the spring to the beam with thread, one space from the pivot. Attach the lower end of the spring to an anchoring mass resting on the ground. The spring should be a little bit stretched. Adjust the tension by altering the length of cord used in securing the spring to the lever or the anchor.
Again there is a clockwise turning effect, or moment, and an anticlockwise moment, which should be the same for balance to be achieved. You can use this system to measure the force exerted by the stretched spring, in terms of weight of the loads. Weight = mass x gravitational field strength (w=mg).