P5 - Inertia And Newton's Third Law Flashcards
What is intertia?
The tendency for motion to remain unchanged
What does an objects intertial mass measure?
How difficult it is to change the velocity of an object
How can intertial mass be found?
Newton’s Second Law = F = ma
Rearranging this gives m = F / a , so inertial mass is just the ratio of force over acceleration
What is newtons third law?
When two objects interact, the forces they exert on each other are equal and opposite
( If you push something, say a shopping trolley, the frolley will push back against you, just as hard. And as soon as you stop pushing, so does the trolley )
How does anything go anywhere?
As the two forces are acting on different objects
EXAMPLE FOR NEWTONS THIRD LAW
When skater A pushes on skater B (the ‘action’ force), she feels an equal and opposite force from skater B’s hand (the ‘normal contact force). Both skaters feel the same sized force, in opposite directions, and so accelerate away from each other. Skater A will be accelerated more than skater B, though,because she has a smaller mass - remember a = F/m.
EXAMPLE OF NEWTONS THIRS LAW IN EQUILIBRIUM
An example of Newton’s Third Law in an equilibrium situation is a man pushing against a wall. As the man pushes the wall, there is a normal contact fore acting back on him. These two forces are the same size. As the man applies a force and pushes the wall, the wall ‘pushes back’ on him with an equal force.
Why is a book resting on a ground not newtons third law?
As the two forces are different types (normal contact force and weight) and both acting on the book.
