It is very rare, especially on Earth, to have an object that is experiencing force from only one direction. A bicycle rider has the force of air friction pushing against him. He has to fight against the friction between the gears and the wheels. He has gravity pulling down on him. His muscles are pushing and pulling inside him and so on and so on.
Even as you sit there, you have at least two forces pushing and pulling on you. The force of gravity is pulling you to the center of the Earth. The chair is pushing up on you so you don’t go to the center of the Earth. So with all these forces pushing and pulling, how do you keep track of them all? That’s where net force comes in.
The net force is when you add up all of the forces on something and see what direction the overall force pushes in. The word “net”, in this case, is like net worth or net income. It’s a mathematical concept of what is left after everything that applies is added and subtracted. The next activity will make this clearer.
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I think that Question 8 is somewhat confusing, and here’s why:
1) It doesn’t tell us which scenario to consider.
2) The first sentence says the rope isn’t moving but then the same sentence says one force is moving down.
3) It doesn’t tell us if the rope is above the ground or resting on it.
This might be a better way of thinking about it – here’s a re-write to #8:
If the rope was slightly off the ground, with gravity pulling it down, what does that tell you about the force you and your friend exerted?
Then we can answer that question like this:
Some of the force you and your friend exerted was pulling the rope up.
Hi Aurora!
Could you please explain to me the answer to number 8? “If the rope wasn’t moving, but you only had one force moving down, what does that tell you about the force you and your friend exerted?” I put that it would mean that me and my friend wouldn’t be pulling (therefore not applying any force.) That would then leave only one force moving down, which would be gravity. Can you explain the answer you put please, and tell me why mine is wrong? I hope you have a great day!
Yes! You got it!
What direction are you pulling 6 and 5 pounds in? If they are complete opposite directions, then you’d move int he direction of the 6 pound puller.
What happens if one person pulls 6 pounds and the other person pulls 5 pounds on the rope?
And is that how someone wins a tug-of-war?
What happens if one person pulls 6 pounds and the other person pulls 5 pounds
Its working! Thanks.
You’re right – in different browsers it doesn’t work as a link! I wonder what’s going on… I’ll have my programmer look at it right away. Sorry for the trouble!
FYI, I have tried on my computer and my tablet with no luck.
Yes, I am logged in and I have been able to download with no problem. I downloaded Net Forces once before and now I can’t. I am able to download Detecting Gravitational Fields and others but not the ones I listed.
Make sure you’re logged in, then try again. I checked all four you mentioned and they are all downloading here. What kind of computer/device and browser are you using? Make sure your computer has the ability to read PDFs also.
I can’t get the “download student worksheet & exercises” to work. This has happened with the Full-force cereal, Building Bridges, and Barrel Roof. I got the Net Forces to work once but now nothing.
The normal force is a contact force that is holding you up when you stand. If a chair is standing on the floor, then the floor is exerting an upward force on each leg of the chair in order to support the weight of the chair. Normal force comes into play not only in reaction to weight, but also with situations like pushing against a wall. The wall pushes back with an equal force in the opposing direction. Does that help?
We are trying to understand Newton’s Third Law of Motion: for every action, there is an equal and opposite reaction. We understand that gravity is pulling us down, but what is the force that pushing us in the opposite direction. You called it normal force. What is normal force? Is it magnetism pushing us away?
I am so glad you’ve asked! This is one of those times when we don’t have enough unique words to express what we mean by “force”.
A force is a push or pull that results from an object interacting with another object. Whenever there is an interaction, you’re going to get forces. Forces only exist as the result of an interaction. There are two broad categories for forces: contact, like frictional, tension, normal, air resistance, applied, or spring forces, and then there’s forces that result from “action-at-a-distance”, like in a magnetic, electrical or gravitational field. This is more of a definition of what force is.
The four fundamental forces of nature describe how individual particles interact with each other, no matter where you observe them interacting in the entire universe. They tell us how the nucleus of an atom hold together, the chemical bonds between molecules, how galaxies stay together, and everything else you can think of. This is more of a bigger-picture of how the forces work together to make up our universe.
The four fundamental forces are:
-Gravity
-Electromagnetism
-Strong nuclear force
-Weak nuclear force.
You named two and the others you listed are derived from those two. For example, friction (or any force from objects touching each other) comes from the electromagnetic force of repulsion of the electrons around atoms. The bonds that hold atoms together, like for an object like a chair or table, are also electromagnetic.
I am attempting to have a basic understanding of this material before launching into it with my children. I am having a hard time integrating the 9-12th textbook material into your lectures and online readings. For the Unit 1 – Mechanics – you (Aurora) list four “fundamental” forces: strong nuclear, electromagnetism, weak nuclear and gravity. How does this relate to the materials from the text, in which they categorize (Chapter 5: Analysis of Forces, p. 152) as: normal, static friction kinetic friction, fluid friction, gravity, electrical and magnetic. Are these actually the “force fields” you talk about? Thanks for your help in putting this together so that I can understand the big picture.
This looked like it wasn’t going to be exciting, but your video offered just the right amount of supporting info to gain interest and spark some really good questions and examples from my boys. They even tied it to our math topics without any prompting! Tonight before bed they asked, “Which science experiments do we get to do tomorrow?” It made my day. Thanks!
wow i didn’t know that!!!!!!!!!