Homework for Chapter 1

1. Homework for Chapter 1 The time it takes a planet to make one complete trip around the sun is called the planet's • Orbit • Revolution • Rotation • Period

2. Homework for Chapter 1 The ptolemaic system fulfilled the requirements of a scientific theory because • its explanations of celestial motions, based on observations, resulted in testable predictions • it was presented openly for public inspection when included in Ptolemy's Almagest • it was believed to represent an accurate view of the universe and solar system by religious leaders and learned scholars of the time • it provided a "common sense" explanation concerning the observed motions of heavenly bodies

3. Lecture 3MotionAcceleration of Gravity Chapter 2.1  2.6 Outline • Describing motion (speed and velocity) • Acceleration • Acceleration of gravity

4. Speed is a rate of covering distance Speed, Distance, and Time distance Speed =  time  Average speed d = distance t = time v = speed v=d/t or d=v x t or t=d/v

5. Units Everything measurable is measured in standard quantities called units. In science, the International System (SI) of units is used. The main SI units are: meter (m) – for length second (s) – for time kilogram (kg) – for mass joule (j) – for energy watt (w) – for power Some useful relations: 1 m =100 cm = 3.28 feet 1 km = 0.62 mi 1 cm = 0.39 inch 1 kg = 1000 g = 2.2 lbs 1 lbs = 453 g

6. Units

7. Simple Problems with Unit Conversion How many inches are in 1 km? 100000 cm/2.54 = 39370 in How far is New York from Toledo in km (600 mi)? 1 km = 0.62 mi, 1mi=1.61km 600 mi = 600x1.61=1000 km How heavy is a 150 lbs person in kg? 1 lbs = 0.453 kg 150 lbs x 0.453 = 68 kg

8. Vectors Quantities, which can be described by only a number, are called scalar quantities. Quantities, which are also characterized by direction, are called vector quantities. Speed is a scalar, while Velocity is a vector. Addition of vectors Vector

9. Acceleration Acceleration (a) is a change in velocity and is a vector. vi initial speed vf final speed T  time interval vf vi a =  t Units of acceleration are meters per second per second or meters per second squared (m/s2). Demonstration of acceleration

10. Sir Isaac Newton (1642-1727)

11. The Universal Law of Gravitation gravity Every mass attracts every other mass through the force called gravity The force of attraction is directly proportional to the product of their masses The force of attraction is inversely proportional to the distance between the objects Fg = G x M1x M2 / d2

12. Acceleration of Gravity From our experience, we know that everything falls down. Galileo found that the higher the object when it is dropped, the greater its speed at the ground. It was also found that the acceleration of falling objects is independent of their mass (neglecting air resistance). Acceleration of gravity = g = 9.8 m/s2 If something is dropped from rest, its downward speed will be v = gt.

13. Acceleration of Gravity The downward acceleration g is the same, no matter where an object is thrown. If an object is thrown upward at an angle, it will come to the ground on a curved path called a parabola.

14. Calculating speeds, distances, and times for falling objects If a dropped object initially at rest, its speed v after some time t is v = g x t = gt. If there was an initial speed v0, then v = v0+gt. Distance, which an object travels during time t, is then: d = v0t+gt2/2 Time, during which a resting object will reach the ground, is: t = (2d/g) Example: you will fall off the 3-m UT Rec dive board for 0.8 s.

15. Motion can be described with both scalar and vector quantities. Summary • Speed is a scalar, velocity is a vector. • Acceleration is a rate of changing velocity. • Acceleration of gravity is the same for an object of any mass.