What is a Force? (5 min)

Types of Forces? (8 min)

Newton's Laws (3 min)

Free Body Diagram Fundamentals (15 min)

Steps to Solving Mechanics Problems (7 min)

Free Body Diagrams and 3rd Law Force Pairs (14 min)

Summary

The objective is introduce Newton's laws and apply the fundamentals of a force analysis. Specifically we focus on drawing free-body diagrams to facilitate translating the 2nd law to the mathematical representation. Connections to kinematics are also made.

Atomistic Goals

Students will be able to...

1. Demonstrate the fact that a force is inherently an interaction between two objects or two systems.
2. Explain Newton's 1st law as it relates to inertia.
3. Explain Newton's 1st law and how it relates to the 2nd law.
4. Define static and dynamic equilibrium.
5. Explain Newton's 2nd Law.
6. Explain Newton's 3rd Law force pairs.
7. Define the point particle model
8. Define a system(s) boundary and adhere their analysis to that boundary(s).
9. Identify the type of forces interacting with your system and the direction they are applied.
10. Differentiate between contact and non-contact forces.
11. Demonstrate that the normal force is always perpendicular to the surface
12. Draw a free-body-diagram (FBD) for the system(s).
13. Demonstrate the ability to draw a properly scaled FBD.
14. Draw the coordinate system that reduces the complexity of the vector analysis next to the FBD.
15. Apply geometry to determine appropriate angles for the given coordinate system.
16. Find the components of a force in the chosen coordinate system.
17. Differentiate between A force and a NET force.
18. Apply Newton's 2nd law in the mathematical representation.
19. Differentiate between static and dynamic equilibrium.
20. Differentiate between weight and apparent weight.
21. Synthesize a force and kinematics analysis via the acceleration.
22. Demonstrate that the net force points in the same direction as the acceleration
23. Demonstrate the fact that the net force can be in the opposite direction of the motion.

Khan Academy's Newton's First Law Introduction 2 part video sequence

https://www.youtube.com/watch?v=5-ZFOhHQS68

https://www.youtube.com/watch?v=CQYELiTtUs8

This video from Veratasium explains inertia by discussing why the Earth spins;

https://www.youtube.com/watch?v=TQxeutcYP6I

Watch Doc Schuster's inertia video for further explanations about Newton's 1st Law:

https://www.youtube.com/watch?v=cliJbHYpNic

Other Resources

This link will take you to the repository of other content related resources.

Try your hand at this sledding game after learning about Newton's 1st Law. Hint: It's a lot simpler than you would think!

This simulation discusses Newton's First Law and reference frames:

For additional simulations on this subject, visit the simulations repository.

Pulling a table cloth out from under a stack of dishes,

https://www.youtube.com/watch?v=owOkomofYjU

This NASA video introduces Newton's First Law of motion with many examples.

https://www.youtube.com/watch?v=Q0Wz5P0JdeU

For additional demos involving this subject, visit the demo repository

History of Newton's First Law

https://www.youtube.com/watch?v=HJ79PJq-CWY

This is a concise description of free body diagrams;

Follow along in this interactive tutorial by W.W. Norton & Company about FBD;

Here is a slide show demonstrating how to use free body diagrams with examples

Resource Repository

This link will take you to the repository of other content on this topic.

Newton’s First Law stated simply is: Objects in motion stay in motion unless acted upon by a net external force. Achieving this condition of having no net external forces can mean two things:

1) There are no forces on the object.

2) There are multiple forces on the object, but overall cancel out in every direction.

These situations are the conditions for equilibrium (ignoring rotation which we will cover in PH201). This does NOT mean:

1) The object is not moving, objects can move at a constant non-velocity and still have no net external forces in either of the above conditions. As such, the words “constant velocity” and “equilibrium” should be a trigger words to tell you there is no net force on the system.

• It is often thought that objects in motion will “naturally” come to rest. However, as stated in Newton's first law, an object in motion stays motion unless acted upon by an external force (i.e., A rolling ball comes to rest due to friction).
• Similarly an object at rest stays at rest until it interacts with another object(s) producing a net external force.
• Think about whether an object is in equilibrium (no net external forces); if it is it will continue with the same velocity, magnitude and direction.
• Here's a good Veritasium video that covers what confuses most people about Newtons laws:

https://www.youtube.com/watch?v=TQxeutcYP6I

• Keep everything in SI units as you go.
• The trickiest part of Newton's 1st law is defining the system that you are looking at and determining what an external force is. Drawing a dotted circle around your defined system will help identify internal and external forces.
• Check the units of your answer with the units you would expect for that quantity, for example a force should have units of Newtons (N) which is $\frac{kg*m}{s^2}$.
• The second law is consistent with the first law. If $\sum \vec{F}=0$ then $\vec{a}=0$ and there is no change in the movement of the object.

Multiple Representations is the concept that a physical phenomena can be expressed in different ways. 

Physical

Mathematical

Graphical

Descriptive

Experimental