Action Reaction Pairs

Newton's third law simply states that for every action there is an equal and opposite reaction. ​

So, if object A acts a force upon object B, then object B will exert an opposite yet equal force upon object A.

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​Newton's 3rd Law

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Multiple Choice

According to Newton’s Third Law, action and reaction pairs are equal and opposite. The reason they do not result in zero net force out is because

• The two objects may not be in the same state of motion before they interact.

• They always act at different times

• They always act on two different objects.

• None of these is the reason.

​Action and Reaction Forces Don't Cancel

The forces exerted by two objects on each other are often called action-reaction force pairs. Either force can be considered the action force or the reaction force. You might think that because action reaction forces are equal and opposite that they cancel.

However, action-reaction forces pairs don't cancel becasue they act on different objects.

Forces can cancel only if they act on the same object. ​

Some text here about the topic of discussion

​It didn't let me create a hyperlink. Here is the link play around with the atwood machine.

​ophysics.com/f3.html

F_net=m*a

mg=m_total​*a

(5kg)(10​m/s²)=(5kg+8kg)(a)

50=13a

3.8≈a​

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​Calculating

acceleration

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Multiple Choice

The system shown is released rest. If Friction is negligible, the acceleration of the 4kg block sliding on the table is closest to? (in m/s²)

• 0

• 3.3

• 5

• 10

Multiple Choice

a boy of 500N exerts a force of 200N on a 15,000N boat, as he jumps off the boat into the water. How much force does the boat exert on the boy?

• 300N

• 700N

• 500N

• 200N

Multiple Choice

TRICKY! A postal employee on an elevator goes up and down delivering packages to various floors. During the rides, When is the magnitude the floor pushes on the feet greater than the magnitude of the person pushes on the floor. (Think back to slide 3)

• When the elevator accelerates up

• When the elevator accelerates down

• Its the same because of Newton's 3rd law

Alright!

That was about half the test. Please continuing thinking about the atwood machine!

Good Luck!​

Some text here about the topic of discussion

Draw

Draw a free body diagram on the blue box!

Remember, there in tension, weight, and normal force.

​Remember, this is there is NO

friction! if there was friction we would add an arrow to the left. ​

Answer