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What is Newton's first law?
The Law of inertia: an object at rest remains at rest and an object in motion remains in motion unless a force is applied
What is Newton's second law?
- Acceleration of object is directly proportional to the net force acting on it
- ΣF = ma
- Sum of forces = mass x acceleration
- VERY IMPORTANT EQ
What is Newton's third law?
- When one object exerts a force on another the second object ALWAYS exerts a force on the first object that is equal in magnitude, but opposite in direction
- FAB = -FBA
What is inertia? Mass? Weight?
- Inertia: resistance to a change in motion
- Inertia = Forces / Mass
- Mass: measure of the inertia of an object
- Weight: Fg (the force of gravity) = mg
What is a Newton?
- The unit of force
- kg x m / s2
In a force diagram acting on a pull system with two boxes, what are the forces?
- There is no x motion for either, so the only forces acting are
- Fg and T
- Remember that T is the same for both boxes
- Also remember that direction of acceleration determines +/- values! (one side up will be + and the other side down with be +)
For an incline plane with no friction, what is the normal force? Acceleration?
Static and kinetic friction info
- Static: opposes force on object and prevents movement. The value can vary based on force applied.
- Ffs ≤ μs x FN
- Kinetic: friction during movement, does not change and is not dependent on speed.
- Ffk = μk x FN
- Note - μk typically less than μs
- Note - friction ALWAYS opposes velocity
For an incline plane with friction, what is the normal force? Acceleration?
- FN = mg(cosθ)
- ax = g(sinθ + μk x cosθ)