Best Film on Newton's Third Law. Ever.

There is a gravitational force of attraction between the Earth and the moon, but is it mutual? That is, are the forces on the Earth and the moon equal? Most people would say no, the Earth exerts a greater force of attraction because it is larger and has more mass. This is a situation in which Newton's Third Law is relevant. Newton's Third Law says that for every force, there is an equal and opposite reaction force. So the force the Earth exerts on the moon must be exactly equal and opposite the force the moon exerts on the Earth. But how can that be - that the same size force keeps the moon orbiting, but barely affects the Earth? The answer is inertia - the tendency for all objects with mass to maintain their state of motion. Since the Earth has much more mass than the moon, it has greater inertia and therefore experiences much less acceleration for the same amount of force.

Category:

Education

Tags:

• Newton's Third Law
• Newton's Laws
• gravity
• gravitational force
• inertia
• earth
• moon
• moon's orbit
• force of attraction
• science literacy

[st08st08]

Does that mean we are exerting the same force on the sun, as it does on us?

[1veritasium]

@st08st08 correct.

[plaustrarius]

Is this not closer to the second law? if net force=mass(acceleration), and neither body accelerates towards the other, net force must be zero...right?

[1veritasium]

@plaustrarius This is a good question, but the bodies are accelerating towards each other. In fact there is a net force on each. But the point is the size of the force is the same on each body, which is what Newton's third law says.

[robbymontague]

I just want to say that I love how devoted you are to teaching through this medium. Nothing is ever quite over my head, but is complex enough to remain interesting. Also, you're activity in the comments is commendable.

[1veritasium]

@robbymontague Thank you!

[Ubazr]

1:35  speed limit c . That is a Einstein street .

[vampiracy]

This is actually really good to demonstrate with magnets. Most people will say that a magnet will exert a force on a piece of iron, but the iron will not exert any force on the magnet. However, you can see if the iron is held securely in one position and the magnet is placed nearby, the iron will exert a force on the magnet, closing the distance. Also, if neither the magnet or the iron are secured, they will move towards each other at the same acceleration (assuming no friction or equal weight).

[Chewie443]

A non-scientist's muse: If the mutual attraction between the two bodies is equal and opposite, even when the mass of one body changes drastically and thus increases its attractiveness, then gravity isn't a property of either body but of the relationship between them.

[zelda0is0so0cool]

So I'm exerting the same pull on the universe as it is to me!?!?

AWESOME!

[zelda0is0so0cool]

@1veritasium Mind = blown

[scottmarshall456]

I felt something in my spleen...sure ain't Newton's Third Law though...

[andreirocks1992]

It's funny that if the Moon exerted a smaller force on Earth, it would cause a lot of logical inconsistencies

[LaenPvP]

You're the best! P.S I'm losing weight and i think we look similar, if i look like you when i lose my weight I'll be very happy! (compliment)

[renamorcen]

I literally yelled IDIOTS !

[Viruzzz]

Why do I never bump into these interviewers asking questions to random people on the street? It's nearly always about political opinion or science, opinion can't really be "wrong" and I would ace science!

I guess that would make for a boring video clip though :p

[rlee8807]

Perhaps one of the larger obstacles for people is conceptualizing how multiple laws interact with each other. All three laws could be identified in any given situation.