The upward normal force exerted by the floor is 620 N on an elevator passenger who weighs 650

step 1 Okay, chapter 4, problem 24, we have a person in an elevator. Their weight is 650 newtons. I kno

The upward normal force exerted by the floor is 620 N on an...

The upward normal force exerted by the floor is $620 \mathrm{~N}$ on an elevator passenger who weighs $650 \mathrm{~N}$. What are the reaction forces to these two forces? Is the passenger accelerating? If so, what are the magnitude and direction of the acceleration?

Key Concepts

Newton's Third Law of Motion

Newton's Third Law states that for every action force there is an equal and opposite reaction force. This principle is essential for analyzing interactions between objects, such as the forces between a person's body and the floor of an elevator. It explains that if the floor exerts an upward normal force on the passenger, the passenger exerts an equal but opposite force on the floor.

Normal Force

The normal force is the contact force exerted by a surface to support the weight of an object resting on it. In this context, the upward normal force provided by the elevator floor acts perpendicular to the surface and works against the gravitational pull on the passenger, and any imbalance between this force and the gravitational force can lead to acceleration.

Gravitational Force (Weight)

Gravitational force, often referred to as weight, is the force due to gravity acting on an object. This force is directed downward towards the center of the Earth and is crucial for understanding the balance of forces on an object in a gravitational field, such as the elevator passenger.

Net Force and Acceleration

Net force is the sum of all forces acting on an object, and according to Newton's Second Law, it is directly proportional to the acceleration of the object. When the normal force and gravitational force acting on the passenger are not equal, there is a net force that causes acceleration. Analyzing the difference between these forces determines the magnitude and direction of the acceleration.

Transcript

00:01 Okay, chapter 4, problem 24, we have a person in an elevator.

00:04 Their weight is 650 newtons.

00:06 I know that's their weight, not their mass, because it's in newtons.

00:09 And we've got the elevator pushing up on this person with 620 newtons of force.

00:15 First question, well, one of the questions asks is, is this person accelerating? and if so, which direction? absolutely.

00:21 There is a net force acting downward on this person.

00:24 They are accelerating downward.

00:25 We do not know 100 % what direction they're traveling.

00:28 We need more information.

00:30 The net force only gives us the direction of the acceleration, not the direction of motion.

00:34 All i know is they're accelerating downward.

00:36 They feel lighter, only 620 newtons of their 650.

00:40 Now that's not really the meat of the question.

00:42 They want to know the action -reaction pairs to both of these forces.

00:46 So let's start with the 620.

00:47 And here's what i say.

00:49 The elevator pushes up on the person with 620 newtons of force.

00:53 So what does the person do to the elevator? they're pushing down on the elevator with 620 newtons of force.

01:00 Those are going to be equal and opposite.

01:02 Elevator pushes up on the person, person pushes down on the elevator.

01:06 Action reaction pairs are always equal and opposite, and they always act on different objects, not on the same object.

01:11 One's acting on the person, one's acting on the elevator.

01:15 The trickier one is the 650 -newton weight force, because, hey, here's the earth down here pulling on that person with 650 newtons of force.

01:24 What's the person doing to the earth? pulling up with 650 -newton of force.

01:30 Okay, gravity forces are going to be action reaction pairs...

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