Unit Dynamics Module Newton s Three Laws page 1 of 2 Weight Mass and weight are not the same thing Mass is the amount of material an object contains and weight is the force of gravity exerted on it W m g When an object is not moving the force of gravity is always balanced by an opposing force Mass is the amount of material that an object contains or a measure of an object s inertia The more difficult it is to move an object the more massive it is Weight is the force of gravity exerted on an object Weight is the product of an object s mass and the acceleration due to gravity W m g The unit of weight is the Newton N 1 N 1 kg m s2 What is the force of gravity on a 1 kg mass Recall m the acceleration due to gravity is ag g 9 8 2 s toward the center of the Earth W mg m 1 kg 9 8 2 s 10 N Consider juggling bricks in space Are the bricks heavy If you put them on a scale they float away The bricks appear to be weightless However the bricks have a lot of mass and therefore a lot of force is required to accelerate them The acceleration due to gravity on the Moon is only one sixth of that on Earth A person with a mass of 60 kg weighs about 600 N on Earth and only about 100 N on the Moon This is why astronauts appear to bounce when they walk on the Moon www thinkwell com info thinkwell com Copyright 2001 Thinkwell Corp All Rights Reserved 1798 doc rev 03 29 2001 Unit Dynamics Module Newton s Three Laws page 2 of 2 Weight Consider the forces acting on an object sitting on a table The force of gravity W m g exerts a downward force on the object The table exerts an upward force on the object FOT Because the object is not accelerating Newton s second law says that the net force on an object must be zero The force of gravity must be balanced by FOT www thinkwell com info thinkwell com Copyright 2001 Thinkwell Corp All Rights Reserved 1798 doc rev 03 29 2001
View Full Document
Unlocking...