Measurement of Mass
Mass is a property of matter that does not depend on temperature, pressure, or location in space. It is defined as the quantity of matter contained in a body. The SI unit of mass is kilogram (kg). The range of masses of various objects is shown in the table below:
| Object | Order of Mass (kg) |
|---|---|
| Electron | 10−30 |
| Proton or Neutron | 10−27 |
| Uranium Atom | 10−25 |
| Red Blood Corpuscle | 10−14 |
| A Cell | 10−10 |
| Dust Particle | 10−9 |
| Raindrop | 10−6 |
| Mosquito | 10−5 |
| Grape | 10−3 |
| Frog | 10−1 |
| Human | 102 |
| Car | 103 |
| Ship | 105 |
| Moon | 1023 |
| Earth | 1025 |
| Sun | 1030 |
| Milky Way | 1041 |
| Observable Universe | 1055 |
To measure large masses, such as those of planets and stars, gravitational methods are used. For small masses like atomic or subatomic particles, mass spectrographs are employed. Common weighing balances include the common balance, spring balance, and electronic balance.
Measurement of Time Intervals
"Time flows uniformly forward" – Sir Isaac Newton
"Time is what a clock reads" – Albert Einstein
Time intervals are measured using clocks, with various types including electric oscillators, electronic oscillators, solar clocks, quartz crystal clocks, and atomic clocks. The order of time intervals is shown in the table below:
| Event | Order of Time Interval (s) |
|---|---|
| Lifespan of the Most Unstable Particle | 10−24 |
| Time Taken by Light to Cross Nuclear Distance | 10−22 |
| Period of X-rays | 10−19 |
| Time Period of Electron in Hydrogen Atom | 10−15 |
| Period of Visible Light Waves | 10−15 |
| Time Taken by Visible Light to Cross Window Pane | 10−8 |
| Lifetime of an Excited Atom State | 10−8 |
| Period of Radio Waves | 10−6 |
| Time Period of Audible Sound Waves | 10−3 |
| Wink of an Eye | 10−1 |
| Time Interval Between Successive Heart Beats | 100 |
| Travel Time of Light from Moon to Earth | 100 |
| Travel Time of Light from Sun to Earth | 102 |
| Half-life Time of a Free Neutron | 103 |
| Time Period of a Satellite | 104 |
| Time Period of Rotation of Earth (One Day) | 105 |
| Time Period of Revolution of Earth (One Year) | 107 |
| Average Life of a Human Being | 109 |
| Age of Egyptian Pyramids | 1011 |
| Age of the Universe | 1017 |
- It is essential to distinguish between accuracy and precision.
- Accuracy refers to how close a measurement is to the true value.
- Precision indicates the repeatability or consistency of the measurements.
Practice Questions:
1. What is the most commonly used unit of mass in everyday life?
- (a) Kilogram (kg)
- (b) Gram (g)
- (c) Pound (lb)
- (d) Ton (tn)
Solution: While kilograms are the SI unit, grams and pounds are more commonly used for everyday objects.
2. Which object would likely have the greatest mass?
- (a) A grain of sand
- (b) A car
- (c) A mountain
- (d) A mosquito
Solution: We know mountains are much larger than cars, so they likely have the greatest mass.
3. How would you estimate the mass of a small object like a coin?
- (a) Measure its length with a ruler.
- (b) Hold it in your hand and feel its weight.
- (c) Use a complex scientific instrument.
- (d) Look up its mass in a book.
Solution: Estimating weight by feel is a common way to gauge the mass of small objects.
4. How can we tell if time seems to pass quickly or slowly?
- (a) By looking at the sun's position.
- (b) By measuring the distance traveled.
- (c) By our perception and activities.
- (d) There's no way to tell.
Solution: Our perception of time can be influenced by what we're doing.
5. What kind of clock might you find in a public building?
- (a) Sand timer
- (b) Sundial
- (c) Electric clock
- (d) Water clock
Solution: Electric clocks are common in public buildings due to their reliability.
6. Which event would likely take the shortest amount of time?
- (a) Blinking your eyes
- (b) Running a marathon
- (c) Traveling across the country
- (d) The Earth rotating on its axis
Solution: Blinking is a very quick action compared to the other options.
7. A watch consistently shows a time slightly behind the actual time. Is it accurate?
- (a) No, it's not accurate.
- (b) Yes, it shows the time.
- (c) It depends on how much behind it is.
- (d) It's accurate for old-fashioned time.
Solution: Accuracy refers to how close a measurement is to the true value. If it's consistently behind, it's not accurate.
8. You measure the length of a table three times and get slightly different results. What does this suggest?
- (a) The table is changing size.
- (b) The measuring tool is broken.
- (c) The measurements are not very precise.
- (d) You need to measure more times.
Solution: Inconsistent measurements indicate a lack of precision.
9. Scientists need to find the mass of a faraway planet. What might they use?
- (a) A weighing scale
- (b) A spring balance
- (c) Telescopes and calculations based on gravity
- (d) A mass spectrometer
Solution: We can't directly weigh distant planets. Scientists use telescopes and gravitational observations.
10. What is a key feature for a clock used in scientific experiments?
- (a) Easy to read from afar
- (b) Looks decorative
- (c) Extremely precise and consistent
- (d) Makes a loud ticking sound
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