2. What is a Mass?
Mass is the amount of matter in a body
Mass is a property that does not change with its location or
shape. The SI unit of mass is the kilogram (kg)
What is a Weight?
The weight of an object is the gravitaional force,
or gravity, acting on it
Weight is a force, so its SI unit is the newton (N). The
direction of weight is downward – towards the centre of the
Earth.

3. What is a gravitational field?
A gravitational field is a region in which a mass
experiences a force due to gravitational attraction
What is a gravitational field strength?
Gravitational field strength g is defined as the
gravitaitonal force acting per unit mass.

4. • The weight of an object depends on the
strength of the gravitaional force acting on it.
• On Earth the gravitational field strength is
approximately 10 N/kg.
• 1 kg mass on Earth experiences a force of 10 N

5. Mass and Weight Relation
The weight or gravitaitonal force acting on an object is dependent on its mass.
The more mass an object has, the grater the gravitaitonal force acting on it.
W = mg
W = weight (N)
m = mass of the object (kg)
g = gravitational field strength (N/kg)

6. How is mass and weight measured?
• Weight is measured using electronic
balance, spring balance, bathroom scale,
etc.
• Mass is measured using a beam balance.
Spring balance and bathroom scale
Beam balance

7. Difference between
mass and weight
Mass Weight
• An amount of matter • A gravitational force
• A scalar quantity • A vector quantity
• SI unit: kilogram (kg) • SI unit: newton (N)
• Independent of the
gravitational field strength
• Dependent on the
gravitational field strength
• Measured with a beam
balance or a calibrated
electronic balance
• Measured with a spring
balance

8. Examples
1. The gravitational field strength of Jupiter is 22.9N/kg. An astronaut wighs
1200 N on Earth. Assuming that the Earth’s gravitational field strength is
10N/kg, find out his weight in Jupiter.
Solution:
Mass of astronaut = weight / gravity
= 1200 N / 10 N/kg
= 120 kg
Weight in Jupiter = mass x gravity
= 120 kg x 22.9 N/kg
= 2748 N

9. 2. An object on planet A has a mass of 5 kg. Its weight is 7 N. Find out the
gravitational field strength in planet A.
Solution:
Gravity = Weight / Mass
= 7 N / 5 kg
= 1.4 N/kg

10. 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
What is Inertia?
• Mass is a measure of inertia.
• An object with a greater mass will
have greater inertia.

11. View animation of inertia

12. Density
The density of a material is its mass per unit volume.
What is Density?
The symbol most often used for density is ρ
Formula
ρ = m / V
ρ = density
m = mass
V = volume The SI unit of denstiy is kg m-3

13. Example
1. A brick of salt measuring 10.0 cm x 10.0 cm x 2.0 cm weighs 433 grams.
What is its density?
Solution:
Density = mass/Volume
Step 1: Calculate Volume
Volume = length x width x height
Volume = 10.0 cm x 10.0 cm x 2.0 cm
Volume = 200.0 cm3
Step 2: Determine density
Density = mass/Volume
Density = 433 g/200.0 cm3
Density = 2.165 g/cm3
Answer:
The density of the salt brick is 2.165 g/cm3.

14. The End