Aim: How can we calculate weight Aim: How can we calculate weight (gravitational force)?(gravitational force)?

Sketch the resultant force.Sketch the resultant force.

There are two types of forces. Contact and There are two types of forces. Contact and noncontact forces.noncontact forces.

Contact forces:Contact forces: FrictionFriction TensionTension Applied (push of pull)Applied (push of pull) Normal forceNormal force Air ResistanceAir Resistance

Non Contact Forces:Non Contact Forces: GravitationalGravitational ElectrostaticElectrostatic MagneticMagnetic

Mass-Force-WeightMass-Force-Weight

How can we define mass?How can we define mass?Anything that has matter. (something that we Anything that has matter. (something that we can touch)can touch)Mass is constant no matter where the object is Mass is constant no matter where the object is located in the universe.located in the universe.Mass is measured in kilograms. (kg)Mass is measured in kilograms. (kg)Mass is a scalar quantity. Mass is a scalar quantity. If my mass on Earth is 72 kg, then what is my If my mass on Earth is 72 kg, then what is my mass on the moon?mass on the moon?

72 kg 72 kg

How can we define a force?How can we define a force?A force is a push or pull on a mass A force is a push or pull on a mass

(object).(object).Force is a vector quantity. It needs both Force is a vector quantity. It needs both

magnitude and direction.magnitude and direction.Force is measured in Newtons. Force is measured in Newtons.

Abbreviation (N).Abbreviation (N).

How can we describe weight?How can we describe weight?

Weight is a measurement of the Weight is a measurement of the gravitational force acting on an object.gravitational force acting on an object.

Symbol for weight is FSymbol for weight is Fgg. Formula to . Formula to

calculate weight is calculate weight is

m stands for mass and g stands for m stands for mass and g stands for acceleration due to gravity. acceleration due to gravity.

mgFg

Acceleration Due to Gravity Comparison

Body Mass [kg] Radius [m] Acceleration Due

to Gravity, "g" [m/s²] g / g-Earth

Sun 1.99 x 1030 6.96 x 108 274.13 27.95

Mercury 3.18 x 1023 2.43 x 106 3.59 0.37

Venus 4.88 x 1024 6.06 x 106 8.87 0.90

Earth 5.98 x 1024 6.38 x 106 9.81 1.00

Moon 7.36 x 1022 1.74 x 106 1.62 0.17

Mars 6.42 x 1023 3.37 x 106 3.77 0.38

Jupiter 1.90 x 1027 6.99 x 107 25.95 2.65

Saturn 5.68 x 1026 5.85 x 107 11.08 1.13

Uranus 8.68 x 1025 2.33 x 107 10.67 1.09

Neptune 1.03 x 1026 2.21 x 107 14.07 1.43

Pluto 1.40 x 1022 1.50 x 106 0.42 0.04

ExampleExample

Bob has a mass of 80 kg. Calculate his Bob has a mass of 80 kg. Calculate his weight on the earth.weight on the earth.

2/8.9

80

smg

kgm

NF

smkgF

mgF

g

g

g

784

)/8.9)(80( 2

An 82 kilogram student weighs 1153.74 An 82 kilogram student weighs 1153.74 newtons. Determine the planet that the newtons. Determine the planet that the student is standing on.student is standing on.

How much does Bob weigh on the moon?How much does Bob weigh on the moon? The acceleration due to gravity on the The acceleration due to gravity on the

moon is 1/6moon is 1/6thth of Earth’s. of Earth’s.

22

/6.16

/8.9sm

smgmoon

2/6.1

80

smg

kgm

moon

mg mgF

)/6.1)(80( 2smkg

N128

A person weighs1,826 Newtons on Jupiter A person weighs1,826 Newtons on Jupiter determine the person’s weight?determine the person’s weight?

Acceleration due to gravity on Jupiter is Acceleration due to gravity on Jupiter is 23.12 m/s23.12 m/s22. .

Calculate the acceleration due to gravity.Calculate the acceleration due to gravity.

Force vs Mass

02

468

1012

1416

0 2 4 6 8 10 12

Mass (kg)

Gra

vita

tio

nal

Fo

rce

(N)