Hot or Cold?
Class 6 Science · Chapter 7: Temperature and its Measurement · NCERT Curiosity section 7.1
Learn
Nisha fills three bowls: one with cold water, one with lukewarm water, and one with warm (not hot) water. She puts her left hand in the cold bowl and her right hand in the warm bowl for a minute, then puts both hands in the lukewarm bowl.
Surprise! Her left hand feels the lukewarm water as warm, and her right hand feels the same water as cool. Our sense of touch tells us whether something is hotter or colder than our hand, not exactly how hot it is.
So touch can fool us, and touching very hot things can even burn us. To know exactly how hot or cold something is, we need a reliable measuring tool.
Explore: hotter or colder than your hand?
- Sort each one (don't touch the hot ones!).
Remember
- Touch tells us hotter or colder than our hand, and can be fooled.
- To know exactly how hot something is, we measure it.
Quick check
Why can't we rely only on touch to know how hot something is?
- Touch compares with our hand and can be fooled
- Our hands never feel heat
- Touch is always exact
- Hot things cannot be measured
Answer
Touch compares with our hand and can be fooled. The same lukewarm water felt warm to one hand and cool to the other.
Think about it
On a cold morning, a steel railing feels much colder than a wooden bench next to it, though both are in the same air. Can you guess why?
One answer
Both are actually at about the same temperature. Steel takes heat away from your hand much faster than wood, so it feels colder. Touch is judging heat leaving your hand, not the real temperature.
Practice
Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.