Newtons 3rd Law of Motion - Forces in Pairs

​Newton's 3rd Law of Motion

&

Gravity​

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​What is Newton's 3rd Law?

• ​Newton's 3rd Law of Motion states that, "Whenever one object exerts a force on a second object, the second object exerts equal and opposite force on the first object.

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• We call this the law of action/reaction

​Do forces act alone?

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​NO! We talked about forces acting in pairs in Newton's 1st and 2nd Law. Forces always act in pairs, this something we have to remember!

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What forces are acting on you now as you sit in your chair?

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Multiple Choice

Newton's 3rd Law of motion states that....

• A object in motion/rest stays in motion/rest until it is acted upon by an unbalanced force.

• Force is equal to the mass and the acceleration of an object.

• For every action there is an equal and opposite reaction.

Multiple Choice

How do forces act on an object?

• They usually act alone

• They act in pairs

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https://www.youtube.com/watch?v=ZkVU-bj9bDk

​Newton's 3rd Law in space!

Newton's Third Law

​Action and Reaction forces: These two forces are equal in size and opposite in direction

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Explain the action reaction pairs happening in the picture!​

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Multiple Choice

How is this an example of Newton's Third Law?

• Only the ball is applying a force to the soccer players head

• Only the soccer players head is applying the force to the ball

• The are both exerting an equal force on each other

Multiple Choice

When a small car pushes a big truck, the truck applies an equal and opposite force on the car

• True

• False

Open Ended

When the tennis ball is dropped and hits the ground why is it that the ball bounces back to you hand?

Multiple Choice

When a cannon fires a cannonball we observe Newton's third law. Which is the reaction force?

• The cannon moving forward

• the cannon moving backwards

• the cannonball moving backwards

• The cannonball moving forward

Multiple Choice

A book rests on a table.  The force of gravity pulls down on the book with a force of 20 newtons. What prevents the books from accelerating downward ?   

• The table presses back up on the book with an equal and opposite force of 20 newtons.

• The table presses back up with a force greater than 20 Newtons

• The tale and the book together are accelerating downwards at 9.8 m/sec2

• The inertia of the book holds it up

Poll

How do we feel about Newton's Third Law of Motion

• I'm feeling great, because I'm a pro

• I'm a little confused but I think I pretty much have it figured out

• I'm lost... point blank period

• What class is this?

Multiple Choice

The units of force are:

• Joules

• Newtons

• Newtonmeters

• Newtons per meter squared

​Gravity

​Gravity is an attractive force that exists between any two masses. It depends of the mass of the objects and the distance between them

​g is the acceleration due to gravity.

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On Earth that is 9.8 m/s²​

NOTICE

MASS STAYS THE SAME!!! An object's mass will be the same, no matter where it is or how much gravity there is.

Multiple Select

SELECT ALL THAT APPLY

How are mass and weight different?

• mass never changes

• weight depends on gravity

• mass depends on gravity

• weight never changes

Equation w = mg

how to solve various problems

Multiple Choice

What is acceleration due to gravity on Earth?

• 98 m/s²

• 9.8 m/s²

• 0.98 m/s²

Multiple Choice

If a bike has a mass of 10.5 kg, how much does it weigh on Earth?

• 102.9 N
• 1.07 N
• 10.5 N
• 0.93 N

Multiple Choice

The Mars Rover Curiosity weighs 8810.2 N on Earth. Determine Curiosity's mass.

• 899 kg
• 86,339.96 kg
• 0.001 kg
• 8810.2 kg

Multiple Choice

If an object weighs 35 N on Saturn, what is the mass of the object if gravity is equal to 10.44 m/s²?

• 3.35 kg
• 365.4 kg
• 0.298 kg
• 35 kg

Multiple Choice

If a 75 kg TV is taken to Venus, where it weighs 665 N, what is acceleration due to gravity on Venus?

• 8.87 m/s²

• 49,875 m/s²

• 0.11 m/s²

Multiple Choice

An astronaut has a mass of 100 kg and has a weight of 370 N on Mars. What is the gravitational strength on Mars?

• 37,000 m/s²

• 3.7 m/s²

• 0.27 m/s²

Multiple Choice

How much does Captain America weigh if he has a mass of 86.18 kg?

• 844.56 N
• 86.18 N
• 8.79 N
• 0.11 N

Multiple Choice

Captain America and the Avengers follow the Chitauri back to their home planet, Chitauri Prime. If gravity on Chitauri Prime is rumored to be 8.76 m/s², how much will Captain America weigh there? (Remember, his mass is 86.18 kg)

• 754.94 N
• 9.84 N
• 0.10 N
• 86.18 N