Topic 1: Motion, Forces & Energy

1.3: Mass and Weight 

Definitions: 

-Mass is a measure of the quantity of matter in an object at rest relative to the observer.

-Weight is a gravitational force on an object that has mass. 

-Gravitational field strength is the force per unit mass. 

Mass: 

-SI unit: Kilograms or kgs 

-Scalar quantity (has magnitude but no direction) 

-Doesn’t change at different locations 

-The greater the mass of an object, the more difficult it is to speed it up, slow it down, or change its direction 

-Measured by a top-pan balance. 

Weight: 

-SI unit: Newton (N) 

-Vector quantity (has both magnitude and a direction) 

-Changes as the gravitational force changes. 

-Because of weight: objects stay firmly on the ground and will always fall to the ground.

-Measured by a spring balance, or a newton meter 

Gravitational Field Strength: 

-Equivalent to the acceleration of free fall, 9.8 m/s² 

● W=mg

-Where W is the weight, m is the mass, and g is the gravitational force acting on that object 

-An object in free fall in a vacuum, in a uniform gravitational field, will accelerate at a rate also known as g. 

Written by: Hiba Shakeel, Head of Physics at SimplifyIGCSE

Curated and uploaded by: Yassein Abdoun