newton’s first law
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Newton’s First Law. Level 1 Physics. CHAPTER 4 ESSENTIAL QUESTIONS. What are Newton’s Laws of Motion? How do forces cause motion? How can the Law of Universal Gravitation be applied? How can one weigh the earth? What effect does friction have on the motion of an object?. - PowerPoint PPT PresentationTRANSCRIPT
Newton’s First LawLevel 1 Physics
CHAPTER 4ESSENTIAL QUESTIONS
What are Newton’s Laws of Motion?
How do forces cause motion?
How can the Law of Universal Gravitation be applied?
How can one weigh the earth?
What effect does friction have on the motion of an object?
OBJECTIVES FORNEWTON’S LAWS
Force FactsBasic definition: a push or a pull
Can we do a better job? Probably.
An interaction between bodies.
Forces can be classified by two types;1. Contact Force
i.e. Normal, Tension, Friction
2. Field Force (at-a-distance)i.e. Gravitational, Magnetic, electric
Newton’s First LawThe Law of Inertia
The natural tendency for all objects is motion
Newton’s First Law (N.F.L.) An object remains at rest or in a state of motion at constant speedalong a straight line unless compelled to change that state by a net force (F).
Forces are balanced
Object at rest vo = 0 m/s
Stays at rest
a = 0 m/s/s
Object in motion v0 0 m/s/s
Object in motionSame speed/direction
a = 0 m/s/s
InertiaInertia – Tendency to resist motion
The more massive an object is, the more inertia it will haveIt is harder to get boulder in moving (also harder to stopthe boulder from moving) than it is to bet a pebble moving
Inertia is a quantity that is dependent upon the mass of the object
Free Body Diagrams(FBD)
A pictorial representation of all of the forces acting on an object
N
T
mg
f
T
mg
Normal force (N): Surfaceforce that is always drawnperpendicular to thesurface
Weight (mg): Always drawnStraight down from center
Tension (T): Force inropes/chains drawnaway from object
Friction (f): Drawn opposing motion
FBD for slopes
mg
Nf
A 10-kg box is being pulled across the table to the right at a constant speed with a force of 50N.
a) Calculate the Force of Friction
a) Calculate the Force Normal
mg
N
Ff €
F = f = 50N
€
mg = N = (10)(9.8) = 98N
Example
Suppose the same box is now pulled at an angle of 30 degrees above the horizontal.
a) Calculate the Force of Friction
a) Calculate the Force Normal
mg
N F
f 30
€
Fx = F cosθ = 50cos30 = 43.3N
f = Fx = 43.3N
Fx
Fy
€
N ≠ mg!
N + Fy = mg
N = mg− Fy →(10)(9.8) −50sin30
N = 73N
Example
A Final Note