LSCPHYS1: MEASUREMENTS IN PHYSICS Assignment 2

Exercise 1

Estimate the area of a table top at home or at school. Then measure the sides and calculate the area. How good was your estimate?

How would you measure the area of irregularly shaped figures or of figures which differ in shapes? For example, how would you measure the area of your hand? Compare your hand with that of your friend who has a bigger or smaller one, and explain how you would get the area of your hand.

Exercise 2

Estimate the area of your palm and design an investigation to measure the area of your palm.

Hint: You can use a graph paper

Note: Regular shapes such as square, rectangle, triangle and circle have a formula for calculating their area. Write down the formula for calculating the area of these shapes. You did this work in the Primary school Mathematics.

Measuring mass

 What you need

• A pen, exercise book, ruler, small stones,
• Beam balance

What to do

Measure and record the masses of each of the materials provided. One litre of pure water has a mass of one kilogram. So if you do not have 1-kg mass for the next activity, you can use a 1-litre bottle of water.

Activity 2.4: Estimating the mass of an empty 20-litre jerry can

Key question

What is the mass of an empty 20-litre jerry can?

What you need

• A beam balance reading up to 1 kg
• 1 kg mass
• 20-litre jerry can
• 100 g mass

What to do

1. Hold the 1 kg and 100 g masses to get some idea of how heavy they
2. Estimate how heavy your 20-litre jerry can
3. Check your estimate by weighing the 20-litre jerry can on the beam
4. Was your estimate close to the actual mass?
5. Repeat the experiment with something much lighter, such as your plastic Then repeat it with something much heavier, such as yourself.

The mass of small objects such as your plastic mug is usually measured in grams. The mass of larger objects such as your 20-litre jerry can or yourself is usually measured in kilograms.

Question:

What is the likely source of error in the measurement of mass in activities 2.3 and 2.4? How can they be minimized?

Activity 2.5: Interconversion of units of volume

Key question: How many cm3 are in 1m3?

What to do

1. Convert 1 m to
2. Multiply 1 m by 1 m by 1 m to 1 m3.
3. Multiply also 100 cm by 100 cm by 100 What do you get?
4. Compare the volume in m3 to the volume in cm3.
5. Then convert 200 cm3 to m3.

Activity 2.6: Finding the volume of a classroom

Key question

What is the volume of your classroom?

What you need

• Ruler or tape measure

What to do

1. Estimate the length and width and height of the room and find their product to estimate the volume of the Compare your answer with that of a friend.
2. Now measure these with a ruler or tape measure and calculate the real volume of the How close was your estimate? Did you do better than your friend? What could have caused a difference in your readings?

Fig. 2.10: Illustration of measuring volume of a classroom

Activity 2.7: Finding the volume of a liquid

Key question

How can we measure the volume of a liquid?

What you need

• Small bottle containing water
• Measuring cylinder

What to do

1. Estimate the volume of the liquid in the bottle in litres, millilitres and cubic
2. Pour the liquid into a measuring Remember to read the bottom of the meniscus.

Fig. 2.12: Position of eye while measuring using a measuring cylinder

Can you make your own measuring cylinder out of a plastic bottle?

How accurate can it be?

NOTE: For more accurate and specific measurement of the volume of liquids, a burette and a pipette are used. These instruments are fragile and should be handled carefully.

Activity 2.8: Measuring volume of an irregular object

Key question

How can we find the volume of a stone or any other irregular object?

What you need

• Measuring cylinder
• Water
• Stone (small enough to go into the measuring cylinder)

What to do

1. Estimate the volume of the
2. Put some water in the measuring cylinder and read the volume (x cm3) .
3. Put the stone in the water in the cylinder and read the new volume (y cm3).
4. The difference between the two volumes is the volume of the

The stone in the above activity has a volume of 50 cm3. How good were you at estimating the volume? What could have caused an error in the measurement?

You can use the stone to measure the volume of an object that floats, such as a small piece of wood. First find the volume of the stone with a rubber band round it. Then attach the piece of wood to the stone with the rubber band. Then find the volume of the stone and the wood fastened together in the same way.

Finally, subtract the volume of the stone (and rubber band) that you found first from the volume of the stone and the wood fastened together.

Exercise 2.3

State the most appropriate units in which you can express the following times

1. Your age
2. The time it takes to drink a cup of tea
3. The time the school assembly takes
4. The gestation period of a goat