Why scientists use tools
Your senses are amazing, but they can be fooled. Is the water warm or just warmer than your hand? Is this rock heavier, or does it just look bigger? A tool helps you get an exact, trustworthy answer that someone else can check.
Scientists around the world use the metric system. It is based on tens, which makes it easy to change from one size of unit to another.
Measuring length
Length tells how long, wide or tall something is.
| Unit | Symbol | About the size of |
|---|---|---|
| millimetre | mm | the thickness of a dime |
| centimetre | cm | the width of your fingernail |
| metre | m | one big step |
| kilometre | km | a 10–15 minute walk |
- 10 mm = 1 cm
- 100 cm = 1 metre
- 1000 m = 1 km
Use a ruler for small things, a metre stick or measuring tape for bigger things.
Measuring mass
Mass tells how much matter is in something. We measure it with a balance or a scale.
- A gram (g) is about the mass of a paper clip.
- A kilogram (kg) is 1000 grams, about the mass of a 1-litre bottle of water.
Measuring volume
Volume tells how much space something takes up. For liquids, use a measuring cup or a graduated cylinder.
- A millilitre (mL) is a few drops.
- A litre (L) is 1000 mL, the amount in a large water bottle.
When you read a graduated cylinder, look at it at eye level. Read the bottom of the curved surface of the water, called the meniscus.
Measuring temperature
A thermometer measures how hot or cold something is. Scientists use degrees Celsius (°C).
| Temperature | What it means |
|---|---|
| 0 °C | Water freezes |
| 20 °C | A comfortable room |
| 37 °C | Normal body temperature |
| 100 °C | Water boils |
Seeing small things
A magnifying glass makes small things look bigger. It helps you see the hairs on a bee’s leg or the crystals in a rock. A microscope makes things look hundreds of times bigger, so you can see tiny cells.
Other handy tools
- Stopwatch: measures time in seconds and minutes.
- Spring scale: measures force in newtons.
- Rain gauge: measures how much rain fell.
- Compass: shows which way is north.
Always write the unit
Every measurement needs a number and a unit. "The plant grew 4" doesn’t tell us much. Four what? "The plant grew 4 cm" is clear.
Using tools safely
- Wear safety goggles when working with liquids.
- Never taste anything in a science lab.
- Handle glass carefully and tell an adult if anything breaks.
- Never look at the Sun through a magnifying glass.
Common mistakes
- Starting at the end of the ruler instead of at 0.
- Reading a cylinder from above instead of at eye level.
- Mixing units, such as adding 5 cm and 2 m without converting.
Try it yourself
- Measure the length of your shoe in centimetres.
- Find the mass of an apple on a kitchen scale in grams.
- Measure 250 mL of water in a measuring cup.
- Use a thermometer to find the temperature of tap water, then ice water.
- Record everything in a table with units.
Quick recap
- Tools give exact measurements that others can check.
- Scientists use metric units: metres for length, grams for mass, litres for volume.
- A thermometer measures temperature in °C.
- A magnifying glass or microscope helps us see small things.
- Every measurement needs a unit.