Hi, I'm going to show you how to calculate the forces on a person in an elevator that's accelerating downward. So start by giving you some information. We have that the person has a mass of 80 kilograms and they are accelerating downward at 2 meters per second squared. So in a conventional coordinate system, the downward acceleration would be negative to meters per second squared. Okay, so from that data, I should be able to calculate the forces on the person. I'm going to start with a free body diagram. So even though I didn't explicitly make the free body diagram part of this problem, it's always a good start to make sure you're getting things right. So the acceleration is down, which means that the net force, when we add up the forces, they must also point down. So that little bit of information will help guide the free body diagram. The first force I start with is the weight force. There is a weight force exerted by the earth on the person downward. And then the floor of the elevator prevents the person from being in free-fall. The acceleration would be negative 9.8 meters per second squared if the person wasn't in the elevator or standing on anything. The floor of the elevator gets in the way. So there is a normal force, which has to be a little bit less to be consistent with this claim right here that the net force is down. So I draw the arrow a little bit smaller. So normal force, let me use F for floor of the elevator exerted on the person. Okay, so this will help inform my calculations and equations using Newton's second law. So I'm just going to write that down. It's really a one-dimensional problem, nothing happening in the x direction. So I just write down that the sum of the forces in the y direction has to equal mass times the y acceleration. Okay, I have a normal force up that's in the positive direction. I have a weight force down, so I put a minus sign in front of that. And then this one I can actually calculate quite easily. That I could have done right from the beginning because I did ask about what the magnitude of each of the forces is. So let's just go ahead and calculate that as an aside. So just use m times g as always to implicit that this situation occurs on Earth. So I throw a 9.8 for g. So remember g is always a positive number. It's not the acceleration. It's the magnitude of the free fall acceleration and it helps you calculate the weight force among other things. So I throw those numbers into my calculator and I get an answer rounding a little bit of 700 and 80 Newton's. Okay, so I'm halfway there. I've got the weight force. Now I just need to calculate the normal force. So I just add weight to both sides and then throw in the numbers. So I have mass of 80 acceleration. So remember it's down in the negative direction and then the weight is 780. So I throw that into my calculator or maybe you can even do this in your head. I get 620 Newton's. Okay, so there you have it. One dimensional Newton's second law situation calculated both of the forces on the person. Okay, thanks.