PHY 105- Ch. 2 Week 1-2
PHY 105- Ch. 2 Week 1-2 PHY 105
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This 6 page Class Notes was uploaded by Brianna Ja'Niece on Monday September 12, 2016. The Class Notes belongs to PHY 105 at Washtenaw Community College taught by Weishu Bu in Fall 2016. Since its upload, it has received 4 views. For similar materials see Conceptual Physics and Lab in Physics at Washtenaw Community College.
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Date Created: 09/12/16
Chapter 2 Newton’s First Law of Motion- Inertia (Every object in a state of rest or of uniform speed in a straight line unless acted on by a nonzero net force)---an object in motion tends to stay in motion Section I.1 Aristotle on Motion (a) Natural Motion i. Dependent on nature’s elements (ex: earth water, air, and fire) ii. Either straight up or straight down iii. Circular with no beginning or end iv. The heavier the object, the faster it should fall (b)Violent Motion i. Resulted from pushing or pulling ii. Externally caused and was imparted to objects iii. Only moved due to a push or pull NOT by their nature Section I.2 Galileo’s Experiments (a) Galileo’s Discovery i) Objects of the same weight should fall to the ground at the same in the absence of air resistance ii) A moving object needs no force to keep it moving in the absence of friction b) Concept of Inertia i) Force is a push or pull ii) Is a property of matter to resist changes in motion iii) Depends on the mass of an object i. Ex: Section I.3 Understanding Mass and Inertia are equivalent (a) Mass is a measure of the amount of matter an object contains i. It is in kilograms(kg)/grams (g), 100g=1kg ii. The mass of an object remains the same unless matter is added or removed b) Inertia is a measure of an object’s ability to resist changed in its motion i. Measures in kilograms Section I.4 Net Force and Vectors (a) Net Force i) The combination of all forces that change an object’s state of motion i. EX: if you pull on a box with 10 N and a friend pulls oppositely with 5 N, the net force is 5 N in the direction you are pulling b) Vector Quantity i) A quantity whose description requires both magnitude (how much) and direction (which way) ii) Can be represented by arrows drawn to scale called vectors i. Length of arrows represent magnitude and arrowheads shows direction (ex: force, velocity, acceleration) iii) The unit of weigth is the Newton (N) iv) Force of gravity (weight) can change with location v) The force of gravity on the moon is 1/6 of the force of gravity on earth vi) On earth a box has a mass of 12kg and a weight of 120N vii) On the moon it has a mass of 12kg and a weight of 20N viii) Scalar quantity is described by magnitude only NOT involving direction (mass, volume, and speed) ix) If vectors act in the same direction they add, if opposite direction they subtract x) The sum of two or more is called resultant solved by using the parallelogram rule Section I.5 The Equilibrium Rule (a) Mechanical Equilibrium i. The vector sum of forces acting on a non-zero accelerating object equals zero ii. E stands for “the vector sum of” and F stands for “forces” iii. Vector quantities take direction into account iv. If upward forces are +, downward ones are -, and when added they actually subtract v. No motion net force=0 not moving at rest (Bob and Joe on their painting sign scaffold. The sum of the upward tensions is equal to the sum of the weights plus the weight of the scaffold. The magnitudes of the two upward vectors equal the magnitude of the three downward vectors. The net force on the scaffold is zero, so we say it is in mechanical equilibrium) Section I.6 Support Force (a) Normal Force i. Support force (normal force) is an upward on an object that is opposite to the force of gravity Section I.7 Equilibrium of Moving Things (a) Equilibrium i. A state of no change with no net force acting ii. Dynamic Equilibrium no changes in motion net force=0 continues to move but speed does not change and direction does not change
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