The Difference Between Mass and Weight

There is a common perception that weight and mass are basically the same thing. This video aims to tease out the difference between mass and weight by asking people what makes a car difficult to push. The standard answer is that it is difficult to push because it's heavy. But heaviness is a measure of weight, the gravitational pull of the Earth attracting the car to Earth's center. When the car is pushed on a flat road, the force of gravity does not oppose the motion. Instead the resistance felt is an indication of the car's mass which determines its inertia. Inertia is the property of matter that means it tends to resist acceleration - the greater the mass, the less the acceleration for a given amount of force.

[AresTW]

"Weight is mass in a gravity" Shortest definition I heard of it.

[NeilCrabbe]

I remember the example I was given for this years ago. The idea is that an astronaut on the moon lifts up a big rock and because it weighs less than on earth he finds he can lift it with little trouble. So he decides to see how far he can kick it and breaks his toe because the inertia is the same as it would be on earth. Nice example, I thought.

[veritasium]

Yup, no one mentioned friction so I didn't deal with this, but I intended too. Think about pushing a car to get it going and then running in front and pushing it back to stop it. Now friction is helping you, but it's similarly difficult to accelerate as it is to decelerate. Cars really have very little rolling friction. Mu times the normal force doesn't really apply to something with wheels.

[pikdame]

Inertia totally is Dereks favourite word :)

[rrmyjj]

Inertia is why you do not want to get up in the morning in bed

[fanthomans]

Inertia is really hard to get your head around and I love how you put a lot of effort to make people understand it. The problem is based on the wrong concepts in everyday life which children learn during their early years. And the education system in their later years can't really change their misconceptions correctly as we can see in your videos.

[matthewferris]

Did anyone notice the ghost car at 2:50??

[veritasium]

that's a good question. I have certainly been thinking about it recently... No plans just yet but perhaps

[Xidnaf]

I would have said that the difficulty in pushing the car is more due to friction, which is caused by the car's weight, then by the car's inertia.

[CandidDate]

If you go to church, you have mass. If you're patient, you weight.

[MrValdasJ]

It`s amazing how you can make these videos that forces a viewer to think himself and keep guessing and come to right conclusion. bravo sir

[tombombadil]

i would have questioned the friction on the wheels bearings tho. that was never mentioned. but with a bit more googling, it seems ball bearings are very effective at reducing friction

[veritasium]

@edgarsucar I disagree. I was going to talk about this misconception too but not enough people mentioned it in interviews. Think about trying to stop a rolling car moving on a level surface. Now friction helps you but it's similarly difficult to stop as it is to get going. Inertia is the main effect, friction is secondary.

[nripeshdhungana]

It's because of:
1. Inertia
2. Its mass
3. Its weight
4. Frictional force

[wlee]

That is a great way to explain it! I'm using this video. Thank you, Derek.

[dwightschrute]

I love how the guy at 2:37 just randomly threw in the word "momentum", to act like he knew what she was talking about.

[itslucaxbitch]

There still seems to be some confusion.. Okay if you still don't get it : 
1.) All matter has mass, mass is a fundamental property and it's measured in Kilograms (yea.. in pound too..). 
2.) Weight is a force due to gravity, it is equivalent to your mass times the gravitational pull of the planet. You will weigh less on moon than you do on earth.  
3) Inertia is more or less a concept, it does not a have a unit associated with it. Inertia is directly proportional to the mass. More the mass, more the inertia, more difficult the object is to move. 
4) Weighing machines weigh your weight (Newtons) then convert it into KgF (dividing it with 9.8). It measures weight but shows something more closer to mass, so it's safe to put a kG behind it (yea.. or pounds..). 

[veritasium]

@HeyyLookItsAlex I got the car moving and then tried to stop it. Now friction is helping you but it's just as hard to stop it as it was to get it going. Plus we know that cars have very little rolling friction because they can go quite a ways just coasting.

[awesomedaltonkids]

Weight is relative and mass isn't. Your weight on the moon is less than earth but your mass is the same. Its not semantics, they're different concepts.

[AtharvaVaidya]

I've been watching you since a while. Didn't realise how long until I realised I saw this video when it just came out and this was when I was already hooked to your channel. I hate that you and I grew up 😂 thank you for the years of beautiful science (emphasis on physics) content.