So now we have an idea of what forces are and how they affect an object's motion from
Newton's 1st and 2nd laws.
But how do two objects interact with each other? Why does an object stop falling when it hits the ground?
Why don't you pass through a chair when you sit down? And if you lean against a wall, how does the wall know how much force to
exert on you so you don't move?
In this lesson we'll learn about Newton's 3rd law of motion. We'll cover contact force pairs (forces between two objects that are
touching) and non-contact force pairs (forces between two objects that are a distance apart).
Newton's 3rd Law of Motion: If object A exerts a force on object B, then object B exerts an equal and opposite force on
object A (the force is equal in magnitude and opposite in direction).
We'll also learn why two solid objects don't pass through each other: the normal force.
Don't let the name fool you, this is no ordinary force.
It's called a "normal" force is because it always acts perpendicular to the surface
and "normal" means perpendicular in geometry.
A normal force is simple but also pretty interesting, because its magnitude can change due to other forces.
It also affects the
friction force
acting on an object.
Newton's 3rd Law of Motion (14:02)
1
0
:
4
4
Newton's 3rd law of motion
2
:
5
9
Contact force examples
4
:
5
6
Non-contact force examples
7
:
2
4
Why don't the forces cancel out?
8
:
5
2
What are equal and opposite forces?
1
0
:
1
8
What is an action and a reaction?
1
1
:
1
8
Why don't we always see the effects of Newton's 3rd law?
So now we have an idea of what forces are and how they affect an object's motion from
Newton's 1st and 2nd laws.
But how do two objects interact with each other? Why does an object stop falling when it hits the ground?
Why don't you pass through a chair when you sit down? And if you lean against a wall, how does the wall know how much force to
exert on you so you don't move?
In this lesson we'll learn about Newton's 3rd law of motion. We'll cover contact force pairs (forces between two objects that are
touching) and non-contact force pairs (forces between two objects that are a distance apart).
Newton's 3rd Law of Motion: If object A exerts a force on object B, then object B exerts an equal and opposite force on
object A (the force is equal in magnitude and opposite in direction).
We'll also learn why two solid objects don't pass through each other: the normal force.
Don't let the name fool you, this is no ordinary force.
It's called a "normal" force is because it always acts perpendicular to the surface
and "normal" means perpendicular in geometry.
A normal force is simple but also pretty interesting, because its magnitude can change due to other forces.
It also affects the
friction force
acting on an object.
