Gravity and Weight Mass and Weight are different

Gravity and Weight Mass and Weight are different. Gravity affects weight, but not mass. Weight is a Force.

First of all…what is gravity? • What holds the book on his head? Gravity. • All objects in the universe attract each other through the force of gravity.

What is mass? Mass is the amount of matter present in an object. The amount of matter present does not change with location. Mass for our purposes, will be measured in kg.

Remember: The formula force: F = ma uses mass measured in kilograms.

Mass is measured on a balance

Balances Are used to measure mass. How much matter is there. When a balance is used, equal amounts of matter (same mass) balance each other out. Gravity does not affect mass because it acts equally on each side of the balance.

Gravity affects Weight is actually a force. Weight is a measure of the gravitational force exerted by an object. Weight is a product of mass and gravitational force. If gravity changes, weight changes. If gravity changes, mass does not change.

Weight on Earth Your weight is a reflection of the gravitational force exerted on you by the Earth. Because Earth is much more massive than you, (and everything else on Earth) the acceleration due to gravity is a constant. Called free-fall acceleration, it equals 9. 8 m/s² on Earth.

Calculating Weight Since F = ma And weight (w) is a force Weight (in Newtons) = mass (m) x free fall acceleration due to gravity (g, = 9. 8 m/s²) SO: w = mg

Weighing in Newtons Suppose a person weighs 50 kg To calculate her weight in Newtons, use the formula w = mg w = 50 kg x 9. 8 m/s² w = 490 N (110 pounds)

How many Newtons? ? ? A) a 5 kg bag of potatoes? B) a 20 kg child? C) a 35 kg dog? D) a 140 kg football player?

How many Newtons? A) a 5 kg bag of potatoes? 5 x 9. 8 = 49 N B) a 20 kg child? 20 x 9. 8 = 196 N C) a 35 kg dog? 35 x 9. 8 = 343 N D) a 140 kg football player? 140 x 9. 8 = 1372 N

But what if g is NOT = 9. 8 m/s² Gravity is based on mass. If mass changes, the acceleration due to gravity changes too. Where would this happen? ? ?

On the Moon, for example.

Gravity on the Moon is 1/6 the gravity on Earth, because the Moon’s mass is 1/6 the mass of the Earth. g on the moon is 1. 6 m/s². So look at those weights again…

How many Newtons on the Moon? A) a 5 kg bag of potatoes? B) a 20 kg child? C) a 35 kg dog? D) a 140 kg football player?

How many Newtons on the Moon? A) a 5 kg bag of potatoes? 5 x 1. 6 = 8 N B) a 20 kg child? 20 x 1. 6 = 32 N C) a 35 kg dog? 35 x 1. 6 = 56 N D) a 140 kg football player? 140 x 1. 6 = 224 N

What about other planets? Planet Mass (kg) Value of g Earth 5. 97 x 10 ^24 9. 8 m/s/s Venus 4. 87 x 10 ^ 24 8. 9 m/s/s Mars 6. 42 x 10 ^23 3. 7 m/s/s Neptune 1. 02 x 10 ^26 11. 0 m/s/s

Compare weights • Earth • 9. 8 m/s² Where would your weight be greater? • Venus • 8. 9 m/s² a) Earth or Venus? • Mars • 3. 7 m/s² • Neptune • 11. 0 m/s² b) Venus or Mars? c) Mars or Neptune? d) Neptune or Earth?

Compare Weights • Earth • 9. 8 m/s² Where would your weight be greater? • Venus • 8. 9 m/s² a) Earth or Venus? • Mars • 3. 7 m/s² • Neptune • 11. 0 m/s² b) Venus or Mars? c) Mars or Neptune? d) Neptune or Earth?

Summary Mass is different from weight. Weight is a force. g = acceleration due to gravity Mass does not change no matter the value of g. Weight is dependent on the value of g. Weight = mass x g