Announcements

1. Announcements • The book “A Tour of the Subatomic Zoo” is at the SU Bookstore,not the Orange bookstore. (The SU Bookstore is the one in Schine) • Frontiers of Science Lecture this Thursday at 7:30, Grant Auditorium. (Benefit of the doubt credits!) “The Elegant Universe” Brian Greene, Columbia University • Lectures will be posted in the morning, so feel free to bring aprinted copy with you to class. Sometimes they will be availablethe night before. • FYI, When printing the PDF file for a lecture, you can print multiple slides to a sheet using the Printer Properties dialog box.

2. Introduction to Physical Quantities

3. Scalars Scalar quantities are those which are described solely by their magnitudeSome examples are: Mass e.g. 14 [kg], 36 [lbs], … Time e.g. 10 seconds, 40 minutes, … Volume e.g. 1000 cm3, 4 litres, 12 gallons Temperature e.g 14 oF , 25 oC, … Voltage e.g. 9 Volts, etc

4. Vectors Vector quantities are those which need to be described by BOTH magnitude and direction Some of the most common examples which we will encounter are: Velocity e.g. 100 [mi/hr] NORTH Acceleration e.g. 10 [m/sec2] at 35o with respect to EAST Force e.g. 980 [Newtons] straight down (270o) Momentum e.g. 200 [kg m/sec] at 90o.

5. Distance • The separation between two locations. • Distance can be measured in many types of units. We will mostly use: MKS Unitsmillimeters [m]centimeters [cm]meters [m]kilometers [km], etc FYI : 1 [km] = 0.6 [mi] • You should be comfortable with converting from [cm] to [m],[mm] to [km], and so on. • We may use the symbolic notation Dd to mean a change in the position. The symbol Dshould be read as “the change in”

6. Time In physics, we are most often less interested in absolute time thanchanges in time, or a time interval. seconds [sec] minutes [min]hours [hr]days years etc… Time can be expressed in several units as well: Example 1: How much time does it take for the earth to make one revolution?Example 2: How long did it take for you to drive to the store today? We usually refer to a time interval as : Dt

7. If a train moves at 50 [meters/sec], how far will it go in 50 seconds ? a) 100 miles b) 2.5 [km] c) 250 [m] d) 2500 miles Velocity Velocity is a measure of the rate of change of the distance with respect to time. v = Dd / Dt • It will usually be measured in [m/sec]. • What does 5 [m/sec] mean? • It means if an object passes by us at 5 [m/sec], it will advance itsposition by 5 [m] every second. So after 2 [sec], it will have advanced 10 [m], and 20 [m] in 4 [sec] and so on.

8. Acceleration (I) • Acceleration is the rate ofchange of velocity with respect to timea = Dv / Dt [a] = [m/sec] / [sec] = [m/sec2] • What does a = 5 [m/sec2] mean? If an object starts at rest, its velocity increases by 5 [m/sec] every second.

9. Acceleration (II) Acceleration can be negative also! We call this deceleration. • If the acceleration is in the same direction as the velocity, the object has positive acceleration (it speeds up). • If the acceleration is in the opposite direction as the velocity, the object has negative acceleration or deceleration (it slows down). Deceleration: Animated GIF of car decelerating

10. What is a Force ? Force is simply: A PUSH or A PULL Forces have both magnitude and direction

11. This is Newton’s Law, and it is often written: F = ma Force and Acceleration • Experimentally, we find that if we apply a forceto an object, it accelerates. • We also find that the acceleration (a)is directlyproportional to the applied force (F) and inversely proportional to the mass (m). That is: Isaac Newton a = F / m • This means: • Increasing the force increases the acceleration; decreasing the force results in a lower acceleration.

12. Force (I) • A force is generally a result of an interaction between two (or more) objects (Try and think of a scenario where a force is applied with only one object involved)? • Can you think of some examples of forces? • Gravitational • Electric • Magnetic • Friction • Wind drag • Van der Waals forces • Hydrogen bonds • Forces in a compressed or stretched spring+…

13. Forces (II) • Since two or more objects must be involved, a force intimately tied to the notion of an interaction. • Interactions are now believed to occur through the exchange of “force carriers”. This is a very important point, and we’ll come back to it later… • So far, we know only of four types of fundamental forces in nature: • Gravity, Electromagnetic, Weak, and Strong • We will come back to each of these • All other forces in nature are understood to be the residual effects of these fundamental forces Particle Exchange and Force (use Explorer)

14. v m p = m*v Momentum (I) What is momentum? Momentum is simply the product of the mass and the velocity.Denoting momentum as p, it is simply: • The units of momentum are [kg][m/sec] == [kg m/sec] • Momentum is a very important subject in physics because it is what we call a conserved quantity. What does this mean? • We will come back to the idea of conserved quantities in physics. They play a very important role in understanding the world around us!

15. -20 [m/sec] 500 [kg] Momentum (Example I) If a 500 [kg] car is traveling west at 20 [m/sec], what is its momentum? A) -1x104 [kg m/sec] B) -1x103 [kg m/sec] C) 25 [kg m/sec] D) 1x105 [kg m/sec] p = mv = (500 [kg])(-20 [m/sec]) = -10,000 [kg m/sec] = -1x104 [kg m/sec]

16. 5000 [kg] 10 [m/sec] Momentum (Example II) If a 5000 [kg] truck is travelling east at 10 [m/sec], what is its momentum? A) -5x104 [kg m/sec] B) 5x104 [kg m/sec] C) 500 [kg m/sec] D) 1x104 [kg m/sec] p = m*v = (5000 [kg])(10 [m/sec]) = 50,000 [kg m/sec] = 5x104 [kg m/sec]

17. 10 [m/sec] -20 [m/sec] 5000 [kg] 500 [kg] Momentum (Example III) If the car and the truck collide, what is the total momentum of the car and truck just before impact? A) 6x104 [kg m/sec] B) -4x104 [kg m/sec] C) 4x104 [kg m/sec] D) 0 [kg m/sec] Since their momenta are aligned in the same direction, we can just add them: PTOTAL = -1x104 [kg m/sec] + 5x104 [kg m/sec] = 4x104 [kg m/sec]

18. Energy

19. What is Energy From Merriam Webster: Energy: The capacity for doing work (or to produce heat)What are some forms/types of energy? 1. Energy of motion (kinetic energy)  2. Heat 3. Electricity  4. Electromagnetic waves - like visible light, x-rays, UV rays, microwaves, etc  5. Mass 

20. Energy • What do you mean mass is a form of energy? • We’ll get to this later…. • The thing about energy is that it cannot be created or destroyed, it can only be transformed from one form into another • Yes, like momentum it is a “conserved” quantity. We willlearn that conserved quantities are a powerful tool in “predicting the future”!

21. Summary I • In nature, there are two types of quantities, scalars and vectors • Scalars have only magnitude, whereas vectors have both magnitude and direction. • The vectors we learned about are distance, velocity, acceleration, force, and momentum • The scalars we learned about are time, and Energy.

22. Summary II • Forces are the result of interactions between two or more objects. • If the net force on an object is not zero, it will accelerate. That is it will either speed up, slow down, or change direction. • Energy and momentum are conserved quantities. This has far-reaching consequences for predicting whether certain “events” or “processes” can occur. • There are many forms of energy. The topic of energy willbe discussed in greater detail in next lecture.