Fig. 1 shows a field scientist placing a rain gauge on a portable stand during a storm survey. The gauge is a tall cylinder, and the stand has four short le...
Question 1 Report
Fig. 1 shows a field scientist placing a rain gauge on a portable stand during a storm survey. The gauge is a tall cylinder, and the stand has four short legs. The scientist presses a metal ring into the ground around the base and adds stones inside the ring. The rain gauge must stay vertical so that the measured volume of water is accurate. Strong winds exert a sideways force near the top of the cylinder. The scientist considers both widening the legs and adding mass low down.
(a) What happens to the centre of mass when stones are added in the metal ring? [1]
(b) Describe the effect of widening the legs on the base of support. [1]
(c) Explain why both changes make the rain gauge harder to blow over. [2]
(d) Give one reason why a vertical rain gauge is needed for a fair measurement. [1]
The figure shows a cardboard cut-out shaped like an irregular island. A student hangs the card from a pin through hole A and draws a vertical pencil line beside a hanging mass. The student repeats the method using hole B. The two drawn lines cross at point X. The card is not uniform in shape, so X cannot reliably be found by simply measuring halfway across the card. The same method could be used for a flat sign made from one sheet of material.
(a) Name the instrument that could be used to produce the vertical line from each hole. [1]
(b) Complete the statement: point X is the card's ________. [1]
(c) Describe why the two lines cross at the centre of mass. [2]
(d) Give one precaution that improves the accuracy of this investigation. [1]
Answer Details
Rain gauge
(a) Adding stones in the ring moves the centre of mass lower, towards the ground. [1]
(b) Widening the legs makes the base of support wider. [1]
(c) The lower centre of mass and wider base mean that a greater tilt is required before the weight line passes beyond an edge. The wind must therefore produce a larger overturning moment to blow the gauge over. [2]
(d) A vertical gauge ensures that the collecting opening has its stated area, so rain is collected consistently for a fair measurement. [1]
Irregular card
(a) A plumb line, or plumb bob, produces the vertical line. [1]
(b) Point X is the card's centre of mass. [1]
(c) When the card hangs freely, its centre of mass lies vertically below the pivot. This is true when suspended from both holes, so the centre of mass must lie where the two vertical lines intersect. [2]
(d) Allow the card to stop swinging before drawing the line. A thin sharp pin or fine pencil lines would also improve accuracy. [1]
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