Free Body Diagrams & 3rd law pair forces.

In summary, the speaker is seeking help on two questions from a practice test paper, as they missed the lessons and have only been studying physics for two weeks. They are unsure about the correct solutions and would appreciate any assistance. They also apologize for any language barriers. In the first question, three forces act on the magnet and the speaker is unsure of their directions and third law pairs. In the second question, two forces act on the pendulum and the speaker is unsure of how many forces act on the orbiting earth.
  • #1
JasonS
1
0

Homework Statement



I have 2 questions from a practice test paper that I can't do (I missed the lessons) - I've attached them, the other questions I did fine. They should be quite basic but I'm not sure if what I'm doing is right (only done physics for 2 weeks). If anyone could correct my current solutions, and/or help on the others that would be great.2. The attempt at a solution

In Q1 (a) I put on weight/reaction force on the magnet... and I know that there would be another force acting on it (from the other magnet) but I don't know where to draw it, or what it would be called.

In Q1 (b) I put the reaction to weight, upwards in direction acting on the earth.

In Q2 (a) I drew tension/weight on the pendulum and just weight on the earth.

Q2 (b) I'm not really sure about.If anyone could help that would be greatly appreciated. Sorry for my English, it isn't my first language. Thanks in advance.
 

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  • #2
JasonS said:
In Q1 (a) I put on weight/reaction force on the magnet... and I know that there would be another force acting on it (from the other magnet) but I don't know where to draw it, or what it would be called.

In Q1 (b) I put the reaction to weight, upwards in direction acting on the earth.
Three forces act on the magnet. What are they and in what direction do they act? What's the third law pair for each force?

In Q2 (a) I drew tension/weight on the pendulum and just weight on the earth.

Q2 (b) I'm not really sure about.
On the pendulum, two forces act. For the orbiting earth, how many forces act?
 
  • #3


First of all, it is great that you are trying to learn and understand physics on your own. Keep up the good work!

To answer your questions, let's start with the basics. A free body diagram is a simplified representation of an object, showing all the forces acting on it. These forces can be either external (acting on the object from the outside) or internal (acting within the object itself). The third law of motion states that for every action, there is an equal and opposite reaction. This means that when two objects interact, they exert equal and opposite forces on each other.

Now, for Q1 (a), you are correct in identifying weight/reaction force on the magnet. This is the external force acting on the magnet due to the gravitational pull of the Earth. The other force that you mentioned, from the other magnet, is the magnetic force. In this case, the two magnets are acting on each other with equal and opposite forces, so you can draw an arrow pointing towards the other magnet, labeled as "magnetic force".

In Q1 (b), you are also correct in identifying the reaction force to weight, which is the normal force. This is the force exerted by the ground on the magnet, in order to support its weight.

Moving on to Q2 (a), you have correctly identified tension and weight on the pendulum. However, you also need to include the reaction force to tension, which is acting in the opposite direction. This is the force exerted by the string on the pendulum, keeping it in circular motion. On the Earth, you can draw the weight of the pendulum acting downwards.

For Q2 (b), you need to consider the forces acting on the Earth due to the pendulum. The Earth exerts a gravitational force on the pendulum, but according to Newton's third law, the pendulum also exerts an equal and opposite force on the Earth. This force can be represented by an arrow pointing upwards, labeled as "reaction force to weight".

I hope this helps you understand free body diagrams and third law pair forces better. Remember, the key is to identify all the external forces acting on an object and to represent them accurately in a free body diagram. Keep practicing and you will get the hang of it in no time!
 

1. What is a free body diagram?

A free body diagram is a visual representation of all the forces acting on an object. It includes both external forces, such as gravity and friction, as well as internal forces, such as tension or compression.

2. How do you draw a free body diagram?

To draw a free body diagram, you must first identify all the forces acting on the object. Then, draw a dot to represent the object and arrows to represent the direction and magnitude of each force. Make sure to label each force with its corresponding symbol.

3. What is the purpose of drawing a free body diagram?

The purpose of drawing a free body diagram is to analyze the forces acting on an object and understand how they affect its motion. By visually representing all the forces, we can apply Newton's laws of motion and solve for unknown variables.

4. What is the Third Law of Motion?

The Third Law of Motion, also known as the Law of Action and Reaction, states that for every action, there is an equal and opposite reaction. This means that when one object exerts a force on another object, the second object exerts an equal and opposite force on the first object.

5. How are free body diagrams and the Third Law of Motion related?

Free body diagrams help us understand the Third Law of Motion by allowing us to see the action and reaction forces as separate entities. By drawing all the forces acting on an object, we can clearly see how they are related and how they follow the Third Law of Motion.

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