# How many newtons does a 3.8 kg backpack weigh on Earth and on the moon?

Asked on by ali2121

ndnordic | High School Teacher | (Level 2) Associate Educator

Posted on

The newton (N) is the unit of force in the SI system.  Weight is considered a force because it is the product of an object's mass and the value for the acceleration of gravity acting on the object.

Mass is the amount of matter in an object and does not change with location.  Therefore, the mass of the backpack will be 3.8 kg on earth and on the moon.

Because the moon is smaller and lighter than earth, its gravity is also weaker.

On earth the acceleration of gravity is 9.8 m/s/s while on the moon the acceleration of gravity is 1.6 m/s/s.

Using the formula for weight: F = mg and substituting the above values you will get:

F = 3.8 x 9.8 = 37.24 N for the weight on earth

F = 3.8 x 1.6 = 6.08 N for the weight on the moon.

kjcdb8er | Teacher | (Level 1) Associate Educator

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A Newton is mass x acceleration. The units of a newton are kg x m /s^2. The acceleration due to gravity on the earth is 9.8 m/s^2. The acceleration due to gravity on the moon is 1.6 m/s^2. The mass of the backpack does not change based on location; so it is always 3.8 kg.

1) 3.8 kg x 9.8 m/s^2 = 37.24 N

2) 3.8 kg x 1.6 m/s^2 = 6.08 N

krishna-agrawala | College Teacher | (Level 3) Valedictorian

Posted on

Weight is a measure of the pull exerted on an object by gravitational pull. The weight is measured in kilograms in S.I.Units. One kilogram weight is defined as the force exerted on one kilogram mass by the gravitational force acting on surface of earth. In kilogram mass is equal to the matter contained in 1 liter of water at 4 degrees centigrade.

The weight of an object, when measured in terms of newtons, is same as the force exerted on it due to gravity. This is equal to mass in kilogram multiplied by acceleration due to gravity.

Using the above insights we calculate the required quantities as follows.

1) Weight on earth:

Weight on earth in newtons = Mass x (Acceleration due to gravity on earth)

= 3.8 x 9.8 = 37.24 N

2) Weight on moon:

Weight on earth in newtons = Mass x (Acceleration due to gravity on moon)

= 3.8 x (9.8/6) = 6.2067 N

Note: Gravitational force on moon is approximately 1/6 times that on earth.

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