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).
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.
Multiple-Choice Questions
Answers
Free-Response Questions
Forces
Free body diagrams
Lab - Discovering Newton's Laws
(Newton's third law, Page 21)
2 carts with spring plunger, assorted masses, meterstick, stopwatch
Holt Physics - Laboratory Experiments
- Newton's 3rd Law of Motion
- Normal Force
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).
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.
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