12. Mass vs. Weight
Success Criteria
Your learning has been successful if you can do the following:
Define acceleration and its units.
Calculate acceleration from speed and time measurements.
Vocabulary
Learn these so you can communicate this concept well.
Average speed: Calculated by the total distance travelled divided by the total time taken for the journey.
Gradient / slope: How steep a line on a graph is.
Speed: How fast an object is moving.
Velocity: Similar to speed, but also tells us the direction in which an object is moving. It includes both speed and direction of motion.
Do Now: on Pg 43 of your SciPAD (find a space!)
From what you know, what is the difference between mass and weight?
Find some space on page 15 of your PESS1.2 SciPAD,
and answer the following questions:
What does each letter in CUTLASS stand for?
First things first... What is Gravity?
Gravity is the force of attraction between objects with mass. It is what keeps us grounded on Earth and governs the motion of all matter in space.
The strength of gravity varies depending on factors like the mass of the objects involved and their distance from each other.
In the illustration below, you can see that as the size of the celestial body (mass) increases, the acceleration due to gravity also increases.
Mass vs. Weight
So what is the difference between mass and weight? Analyse the illustration below.
Mass refers to the amount of matter an object contains - it is a measure of how much "stuff" makes up an object.
The mass of something always remains constant regardless of its location. Whether an object is on Earth, the Moon, or in deep space, its mass remains the same.
Mass is measured in kilograms (kg) or grams (g).
Weight, on the other hand, is the FORCE exerted on an object due to GRAVITY.
Weight varies depending on the gravitational pull acting upon the object. Weight is directly proportional to mass; however, it also depends on the strength of gravity in the object's location (see the section on Gravity below).
Since weight is a force, it is measured in Newtons (N).
Acceleration Due to Gravity
On Earth, the acceleration due to gravity is approximately 9.8 meters per second squared (m/s²), often rounded to 10 m/s² for simplicity. This value determines the weight of an object on Earth's surface.
The mass of Earth is significantly greater than the mass of the Moon. As of the latest data available, Earth's mass is approximately 5.972 × 10^24 kilograms, while the Moon's mass is approximately 7.349 × 10^22 kilograms.
In other words, Earth's mass is over 80 times greater than the Moon's mass. This significant difference in mass contributes to the variations in gravitational pull experienced on each celestial body, with Earth having a much stronger gravitational force compared to the Moon.
The gravity on the Moon is significantly weaker than the gravity on Earth. While the exact value varies slightly depending on location and elevation on the Moon's surface, the average gravitational acceleration on the Moon is approximately 1.625 meters per second squared (m/s²). This is about one-sixth (1/6) the strength of Earth's gravity, making objects weigh much less on the Moon compared to Earth.
