1. Introduction to Physical Science Monday, Wednesday, Thursday Tom Burbine tomburbine@astro.umass.edu

2. Energy Energy is the property of a system that enables it to do work

4. Work Work = Force x Distance

5. To do work You need to move something

6. Energy units In English Units, we use calories to measure energy In science (and in this class), we will use joules to measure energy 1 Joule = 1 kg * m 2 /s 2

7. Joule One joule is defined as the amount of work done by a force of one Newton moving an object through a distance of one meter

9. Calories The small calorie approximates the energy needed to increase the temperature of 1 gram of water by 1 °C. This is about 4.2 joules. The large calorie or food calorie approximates the energy needed to increase the temperature of 1 kilogram of water by 1 °C. This is exactly 1000 small calories or about 4.2 kilojoules.

10. Potential Energy Stored Energy that has potential to do work –Compressed Spring –Drawn bow –Coal –Water in an elevated reservoir

11. Gravitational Potential Energy PE = weight x height PE = mgh –where m is the mass, g is the gravittaional acceleration, and h is the height

12. Kinetic energy Kinetic energy = ½ mv 2 m is mass in kg v is velocity in meters/s Fd = ½ mv 2 Remember: a joule has units of kg * m 2 /s 2

13. How much kinetic energy does a 2 kg rock have if it is thrown at 20 m/s? Kinetic energy = ½ mv 2 A) 200 J B) 400 J C) 40 J D) 800 J

14. Answer KE = ½ * 2 * (20) *(20) = 400 joules

15. Work-Energy Theorem Work is change in kinetic energy Work = ∆KE

16. As the kinetic energy of a system increases, its potential energy decreases by the same amount, and vice versa

17. The change in potential energy is always equal to the change in kinetic energy (assuming there are no other energy losses). Δmgh = Δ½mv 2

21. Kinetic Energy and Momentum Kinetic energy and momentum are properties of moving things Momentum is a vector and capable of being cancelled Kinetic energy is scalar and can not be cancelled Momentum depends on the velocity and kinetic energy depends on the velocity squared

22. Scalars and Vectors

23. Conservation of Energy Energy is neither created or destroyed – it just changes forms Conservation of Energy –The energy in a closed system may change form, but the total amount of energy does not change as a result of any process.

24. Types of collisions Elastic collision – all the momentum is transferred to another object during a collision Inelastic collision – Colliding objects become entangled

25. Momentum and Kinetic Energy Momentum is conserved in elastic and inelastic collisions Kinetic energy is only conserved in elastic conditions Energy is always conserved http://en.wikipedia.org/wiki/Elastic_collision

26. Inelastic Collisions Reduction of kinetic energy Some of the kinetic energy is turned into another form of energy (e.g., thermal energy, sound) http://www.physicsclassroom.com/mmedia/momen tum/cthoi.cfmhttp://www.physicsclassroom.com/mmedia/momen tum/cthoi.cfm

27. Power Power = work done/time interval Units are Watts (Joules/seconds)

28. Any Questions?