NA - Mass Weight Density - E-Learning

Published on: **Mar 3, 2016**

Published in:
Education

- 1. LESSON OBJECTIVES At the end of the lesson, you should be able to: a) State that mass is a measure of the amount of substance in a body b) State that a gravitational field is a region in which a mass experiences a force due to gravitational attraction c) Define gravitational field strength, g, as gravitational force per unit mass d) Recall and apply the relationship weight = mass x gravitational field strength to new situation or to solve related problems e) Distinguish between mass and weight f) State that the mass of a body resists a change in the state of rest or motion of the body (inertia)
- 2. HOW DO YOU MEASURE YOUR WEIGHT? • Bathroom scale • kilograms (kg)
- 3. MASS • Mass is a measure of the amount of substance in a body. • SI Unit: kilogram (kg) • Scalar • Represented by m • Mass does not change wherever the body is.
- 4. WEIGHT • The weight of an object is the gravitational force, or gravity acting on it. • SI Unit: newton (N) • Vector • Represented by W
- 5. WEIGHING MACHINE • Weighing machine measures weight but the units is kg. So what does the weighing machine measure? • Weighing machine measuresWEIGHT. But it is calibrated to display the mass of the body. • How do you calibrate the weighing machine?
- 6. FORMULA Weight (in 𝐍) = mass in 𝐤𝐠 × gravitational field strength (in 𝐍/𝐤𝐠) 𝑾 = 𝒎𝒈 W m g What is gravitational field strength?
- 7. GRAVITATIONAL FIELD & ITS STRENGTH • A gravitational field is a region in which a mass experiences force due to gravitational attraction. • In a gravitational field, a mass experiences a force. • Weight is also known as gravitational force. Earth’s gravitational force acts towards the centre of Earth.
- 8. GRAVITATIONAL FIELD & ITS STRENGTH • The strength of this field is strongest at the surface of Earth and gets weaker farther away. say, 50 N >50 N
- 9. GRAVITATIONAL FIELD & ITS STRENGTH • Definition: Gravitational field strength, g, is the gravitational force acting per unit mass. • Gravitational – an effect due to gravity Field – a region where force is experience Strength – the magnitude of the force • Actual gravitational field strength, g of Earth= 9.80 N/kg. In calculations however, we use 10 N/kg to make it simple.
- 10. ACTIVITY! Find Mr.Wong’s weight on these places! My mass = 100 kg Planet Gravitational field strength, g Weight Earth 10 N/kg Moon 1.6 N/kg Jupiter 24.9 N/kg Pluto 0.6 N/kg Conclusion Weight is dependent on the gravitational field strength of the location. (direct proportion)
- 11. FUN FACT! Planet Gravitational field strength, g Weight Earth 10 N/kg Moon 1.6 N/kg Jupiter 24.9 N/kg Pluto 0.6 N/kg The more massive the object, the greater the gravitational field strength!!! Mass of these planets 5.97 × 1024 kg 7.25 × 1022 kg 1.90 × 1027 kg 1.25 × 1022 kg
- 12. FUN FACT 2!! • Do you know that every object including yourself also have some gravitational field strength? • For a person of 60 kg, his gravitational field strength at 1 metres away ≈ 4 × 10-9 N/kg • Maybe that’s how you attract someone!
- 13. Weight is measured by using spring balances. DO YOU REMEMBER HOW IS WEIGHT MEASURED? Extension Spring Balance Compression Spring Balance
- 14. HOW TO MEASURE MASS? Beam balance with standard masses can be used to measure mass. Since the standard mass experiences the same g, this method can be used on any planet. Beam Balance Electronic Balance Nowadays, the electronic beam is more commonly used to measure mass as it is more accurate and easier to use.
- 15. DIFFERENCE BETWEEN MASS & WEIGHT Differences Mass Weight The amount of substance in a body The gravitational force acting of the body Scalar Vector kilograms (kg) newtons (N) Independent of g Dependent on g Measured with beam balance Measured with spring balance Definition Scalar or Vector? SI Unit Dependence on g Measuring tool
- 16. INERTIA • Mass is a measure of inertia • The inertia of an object refers to the reluctance of the object to change its state of rest or motion, due to its mass. From at rest to moving; or Moving to rest. Changing direction • The greater the mass, the more inertia an object has.
- 17. INERTIA IN ACTION • A MRT train – large mass Time is required to start moving a train. Large braking force is required to stop a moving train. • Wild boar A wild boar is unable to change its direction quickly due to its mass Wild Boar Drill: Zig-zag running pattern allows us to run away from it.
- 18. INERTIA IN ACTION • Oldest trick in the world! http://youtu.be/-cM9S2AzU28 What is the reason the bottles did not move? The bottles have inertia which resists the change of motion. Now watch the video again – Is it real or fake? How do you think they manage to get it done?
- 19. INERTIA IN ACTION Answer: