DO NOW Why doesn t the shot-put move on

DO NOW Why doesn’t the shot-put move on its own?

There Ought’a Be A Law The Laws of Motion

But First A Word About From Our Sponsors Aristotle Galileo Newton

Aristotle Gets It Wrong Born 387 BCE Died 322 BCE Very smart guy. Very famous in his day. Used deductive reasoning for all manner of ideas, not experimentation. Some ideas turned out to be wrong, but hey, somebody has to be first.

Aristotle’s Ideas 370 BCE: Free falling bodies accelerate but heavier bodies fall faster. 370 BCE: Objects need force to keep moving. 340 BCE: Earth is a sphere (Got it right!) 340 BCE: Space is continuous and always filled with matter. 330 BCE: Geocentric cosmology.

Galileo Asks “How” Not Why Born 1564 Died 1642 Curmudgeonly Wanted to be a priest. Points telescope to heavens, discovers Jupiter’s moons. Makes fun of the Pope (bad idea!)

Galileo’s Ideas 1581: Idea of consistent period of a pendulum. 1589: Objects fall at same rate regardless of mass. 1592: Suggests that physical laws of the heavens are the same as those on Earth (Heretical idea!!!) 1592: Primitive thermometer. 1604: Distance for falling object increases as square of time. (d = 1/2 at 2) 1609 to 1610: Moons of Jupiter and observations of the first 6 planets.

Still More of Galileo’s Ideas 1612: Goes beyond Archimedes Principle with theory of hydrostatics. 1613: Principle of Inertia. 1624: Theory of tides. 1632: Supports Copernicus' heliocentric theory by writing The Dialogue (now he’s in real trouble, but not for his support. It’s for a character thought to be the Pope!). 1633: Goes on trial for support of Copernicus in violation of a 1616 agreement w/ The Inquisition. Gets house arrest. Daughter does his penance and dies as a result. 1638: Concept of motion and friction.

But The Story Ends Only Recently On October 31, 1992, 350 years after Galileo's death, Pope John Paul II gave an address on behalf of the Catholic Church in which he admitted that errors had been made by theological advisors in the case of Galileo. He declared the Galileo case closed, but he did not admit that the Church was wrong to convict Galileo on the charge of heresy because of his belief that the Earth rotates round the sun. In effect they pardon themselves and not the “criminal. ”

Newton Asks Why Born 1643 (Coincidence? ) Died 1727 Insane? Brilliant beyond compare. Thought about everything you can think of. Helps Halley win bet with Hooke. Gets into fight with Leibniz.

Newton’s Ideas 1665: Studies the principles of mechanics and gravity, mass and force. 1666: Studies spectrum of light. 1666: Begins work on laws of mechanics and gravitation (at age 23!) 1668: Builds reflecting telescope. 1672: Explains variation of pendulum is due to equatorial bulge.

Still More of Newton’s Ideas 1675: Delivers his theory of light. 1680: Demonstrates that inverse square law implies elliptical orbits. 1684: Universal Gravitation, inverse square law and weight dependence of gravity & mass. 1687: Publishes laws of motion and gravitation. 1687: Publishes analysis of sound propagation. 1704: Publishes corpuscular theory of light and color.

The st 1 Law An object in motion, at a constant velocity or speed – in a straight line – will stay in that motion unless acted upon by an outside force. An object at rest will tend to stay at rest unless acted upon by an outside force. To change an objects momentum requires a force. Simple version – They’ll keep doin’ what they’re doin’ ‘til you make’m do different.

The nd 2 Law Unbalanced forces will cause and object to accelerate. a = F/m For an object to remain in equilibrium, which can mean constant velocity, the net force on an object must be Zero. a = F/m or F = ma ∑F = 0, no change in motion ∑F ≠ 0, change in motion

A Newton Ain’t Just A Cookie Metric unit of mass is the gram, g In physics we use the kilogram, kg The unit of acceleration is m/s 2 F = ma 1 Newton = 1 kg ∙ 1 m/s 2 9. 81 N = 1 kg ∙ 9. 81 m/s 2 W or Fw = mg

The rd 3 Law For every action there is an equal and opposite reaction.

Inertia is a property of matter, just like mass. It is a quantity that defines matter’s resistance to a change in motion. Nobody knows exactly what “it” is. But “it” applies only to linear motion and rotation. To change an objects MOMENTUM requires an unbalanced force (Law-1 and 2).

Momentum is a quantity that helps define what it takes to change an object’s motion. It is a vector quantity. F = ma (i) a = (vf – vi)/t (ii) F = m (vf – vi)/t (iii) Ft = mvf – mvi (iv) p = mΔV (v) impulse = change in momentum

Implications of Impulse = Ft = p = mΔV Consider the difference between punching a pillow and a wall. Which hurts less and why?

Impulse and Time Hitting the pillow hurts less because …. . The longer an impact event takes, the less jarring the acceleration feels. Stopping a car from 60 mph to 0 in 10 seconds has the same total impulse as stopping it in ½ second. t. F F = t

Impulse Management in Car Design Crumple zones increase the time domain of an event and so forces on the occupants are decreased and thus acceleration is reduced.

Conservation Law of Momentum In a collision between objects, the momentum of the objects before the event will equal the momentum of the objects after the event. Innies = Outies m 1 v 1 + m 2 v 2 = m 1 v 3 + m 1 v 4