# What Are the Reaction Forces in These Physics Diagrams?

• Knight226
In summary, for the first diagram, the spring exerts a force to the right on the hand and the wall. For the second diagram, the wagon exerts a force downward on the Earth due to contact and downward to the left on the handle.
Knight226

## Homework Statement

One or more external forces are exerted on each object enclosed in a dashed box shown in the figure below. Identify the reaction to each of these forces. (Assume that (a), (b) and (c) occur on Earth while (c), (d) and (e) occur far from any outside gravitational influences. Select all that apply.)

Pairing reaction

## The Attempt at a Solution

Diagram A shows a hand pulling a spring (see attachment)
The question is
(a) the spring exerts a force
upward on the Earth
to the right on the hand
to the left on the wall
to the right on the wall
to the left on the hand
downward on the Earth

The bold ones is my choice.
For diagram A, the hand is pulling the spring to the right, so, the spring exerts a force to the right of the hand, and to the right of the wall. I think I am very confused with the topic and the way how the words are phrased... when I think of the spring exerts a force to the right of the hand, I am taking the words in as the force exerted by the spring is working against the right of the hand...

The spring exerts a force to the right of the wall (the right is closer to the spring, so the spring has to push back an equal but opposite direction force right?)

Diagram B shows a woman pulling a wagon
The question is
(b) the wagon exerts a force
upward to the left on the handle
downward on the Earth due to gravitational attraction
upward on the Earth due to contact
downward to the left on the handle
upward on the Earth due to gravitational attraction
downward on the Earth due to contact

The bold ones is my choice.

This one I am really confused... I have made 3 selections, but the combination is incorrect.
The woman is pulling the wagon, so there should be an equal force pulling downward to the left on the handle.

Meanwhile, just like how bicycle moves forward because Earth propels it, the wagon exerts a force downward on the Earth due to contact.

I have added "downward on Earth due to gravitational attraction" because gravitational attraction is in play since the wagon is in contact right?...

Thank you in advance.

#### Attachments

• Reaction Force Diagram A and B.jpg
8.3 KB · Views: 1,973
• Reaction Force Question A and B.jpg
26.5 KB · Views: 2,130
a) Assuming the spring hasn't been compressed before, isn't the spring trying to return to its equilibrium position? If so, if you pull a spring right, why would its restoring force vector be in the same direction as the pulling force done by the hand? Try it out. Grab a spring, tie it to something and pull it with your hand. Compare the direction of its restoring force to the direction you are pulling. If you let go, what direction does its restoring force take it?

b) I'd assume there is some friction here, in which case, the "downward to the left on the handle " looks appropriate. You need to identify your forces. If you place an object on a surface here on Earth, what two forces act on it just sitting still on a surface. You probably know gravity is obvious, what is the second force? What direction do those two forces point?

## 1. What is a reaction force?

A reaction force is a force that is exerted in response to an applied force. It is equal in magnitude and opposite in direction to the applied force.

## 2. How is reaction force related to Newton's Third Law of Motion?

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. This means that whenever a force is applied, a reaction force will occur in the opposite direction.

## 3. What are some examples of reaction forces?

Some examples of reaction forces include sitting on a chair (the chair exerts a reaction force to support your weight), pushing against a wall (the wall exerts a reaction force to keep you from falling), and walking on the ground (the ground exerts a reaction force to keep you moving forward).

## 4. How do you identify a reaction force in a given scenario?

To identify a reaction force, you first need to identify the applied force. The reaction force will be equal in magnitude and opposite in direction to the applied force. It will also act on a different object than the applied force.

## 5. Can reaction forces cancel each other out?

No, reaction forces cannot cancel each other out. Since they act on different objects, they cannot directly cancel each other out. However, they can have a net effect of zero if they are acting on the same object from different directions.

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