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Course: Middle school physics>Unit 1

Lesson 3: Action and reaction forces

Action and reaction forces

Review your understanding of action and reaction forces in this free article aligned to NGSS standards.

Key points:

• For every force, there is an equal and opposite reaction force.
• Let’s think about an example: when you push on a box, the box pushes back on you. Your push on the box is the action force. The force from the box on you is the reaction force. The two forces have the same strength, but they act in opposite directions.
• Every force has a reaction force. A force and its reaction are generated together and happen at the same time.

Want to join the conversation?

• I don't really get this concept. How does a box of something else push back on you when you push it?
• Whenever you push on a box, the box pushes back on you with an equal force in the opposite direction. This allows the box to maintain its position and prevents it from moving in the direction that you are pushing it. The strength of the force that the box exerts on you depends on the mass of the box and the amount of force that you apply to it. This is because of something called 'action and reaction'. When you push the object, it is the action, and the object pushing back is the reaction. So, the action and reaction are always equal but opposite in direction.

You might argue that you don't get pushed as far back as the that box
And that's because of friction and mass (which you'll learn later on)

Also, the force of the object pushing back is usually very small. For example, if you push a chair, the chair will push back on you with the same force, but since the chair is so much lighter than you, the force it applies on you will be too small for you to feel. However, if you push a wall, you will definitely feel the reaction force as the wall is much heavier and stronger than you, and since a wall probs wont move you'll be able to apply more force.

It’s alot to understand so don’t worry if you still don’t get it for now, you can always carry on in the course and it might make more sense, or you can ask me another question :)
• a equal force is when the force is balance and a opposite force is a force where if your playing tug a war and the other person is pulling the rope their way is that true
• Yes! If the person lets go of the rope, it will go shooting your way.
• how much jars of peanut butter to carry the empire state building
• 730 Million jars of peanut butter to equal the weight of the empire state building.
• so its like when you toss a ball at the wall this is the reason it bounces back?
• Yes! The ball bounces back because scientifically, it “reflects” off of the surface. Some other examples would be looking at yourself in a mirror or hearing an echo.
• what happens when you push something up a hill ?
• the hill will be pushing back at you (search up newtons third law)
• does gravitational force also have an opposite force ?
• The ground pushes on the object being affected by the gravitational force.
(1 vote)
• how many cups of water would it take to flood the Empire State Building?