Physical Science midterm study guide. Chapter 1 and 2

Transcription

1 Physical Science midterm study guide Chapter 1 and 2 1. Explain the difference between a scientific law and a scientific theory a. Laws generalize observations b. Theories explain observations 2. Select appropriately between a bar graph and a line graph to represent data a. Bar graphs show quantitative differences between qualitative groups, e.g. the average heights of girls and boys. b. Line graphs show change over time 3. Explain the relationship between energy density and the cost of fuel sources a. Higher energy density usually means lower cost b. Lower energy density usually means higher cost c. Give an example of a fuel source with high energy density d. Give an example of a fuel source with low energy density 4. Compare fuel efficiency by calculating % efficiency 5. Convert units a. Seconds, minutes, hours b. mm, cm, m, km c. mg, g, kg d. ml, L Chapter 3 6. Use the equation distance = rate x time to solve word problems 7. Use the slope of a line to find speed on a distance over time plot 8. Use the slope of a line to find acceleration on a speed over time plot 9. Distinguish between average speed and instantaneous speed 10. Distinguish between speed and velocity a. Velocity = speed and direction 11. Calculate acceleration a. a = (v f v i )/(t f t i ) b. When given acceleration, use the equation to find other variables like velocity or time. 12. Describe the motion of an object that has an acceleration of 0m/s Recognize that unbalanced forces cause objects to accelerate, and that balanced forces cause zero acceleration. a. The sum of the forces on an object is the net force 14. Choose a frame of reference. Assign + to one direction and to the other. a. Use this frame of reference to label velocity, forces, and other vectors. 15. Friction a. Describe the difference between static and sliding friction b. Compare the force or air resistance to gravity on a falling object. c. Compare the force or air resistance to gravity on a falling object at terminal velocity. Chapter 4

2 16. Apply Newton s first law of motion a. If the net force acting on an object is zero, the object remains at rest, or if the object is moving, it continues moving in a straight line with constant speed. b. Describe inertia i. Does an object at rest of inertia? ii. Does inertia change with the speed of an object? 17. Apply Newton s second law of motion a. The acceleration of an object is in the same direction as the net force on the object. b. Unbalanced forces cause the velocity of an object to change. c. Force = mass x acceleration i. Explain why objects at rest can still have forces acting on them d. The unit of force is the Newton i. 1N = kg x m/s Describe the gravitational force a. Know the acceleration of gravity near earth s surface = 9.8m/s 2 b. Gravity accelerates all objects at the same right, regardless of their mass c. Interpret the equation for the universal law of gravitation i. F = G(m 1 m 2 )/(d 2 ) ii. The gravitational force between two objects increases with increasing mass iii. The gravitational force between two objects decreases with increasing distance d. Distinguish between mass and weight i. Do you have mass in outer space? ii. Do you have weight in outer space? e. Use the gravitational force to describe projectile motion f. Recognize the sun s gravitational force to be a centripetal force that holds the planets in their orbits. 19. Apply Newton s third law of motion a. When one objects exerts a force on a second object, the second one exerts a force on the first that is equal in strength and opposite in direction. i. Newton s third law explains how rockets can propel themselves through the vacuum of space b. Action and reaction forces do not necessarily cancel out i. The force of a bug on a truck is equal to the force of a truck on a bug, but their masses are so different that they suffer very different fates when they collide on the highway. 20. Solve a sum of the forces question a. F = F 1 + F 2 b. F = sum of the forces, or F net Chapter Explain the relationship between energy and work a. How is work in science different from work in everyday life? 22. Apply the equation for kinetic energy a. KE = ½ mv 2

3 23. Apply the equation for gravitational potential energy a. GPE = mgh b. The SI unit for kinetic energy is the Joule (J) 24. Apply the equation for mechanical energy a. ME = KE + GPE b. The SI unit for potential energy is the Joule (J) c. Potential energy comes in many different forms, examples are i. Elastic potential energy ii. Chemical potential energy iii. Gravitational potential energy 25. Conservation of energy a. Energy can change forms, but it is never created or destroyed b. Electrical energy and chemical energy can both be converted to do work c. Describe the change in KE and GPE of a baseball you throw straight up in the air 26. Distinguish nuclear fusion and nuclear fission a. Fusion is the combining of atoms b. Fission is the splitting of atoms c. Nuclear reactions convert mass into energy. The equivalence of matter and energy means that the laws of conservation of energy and mass are not being broken. Chapter Describe the work being done when motion and the direction of force are a. in the same direction b. at right angles to each other 28. Describe the work being done when there is no motion 29. Apply the equation Work = F x d 30. Power is work over time a. Power = W / t b. The SI unit of power is the Watt (w) c. For energy transfer, power = energy transferred / seconds 31. A machine is a device that makes doing work easier a. Simple machines usually increase the magnitude of output force relative to input force. b. Simple machine can also change the direction of force. 32. In ideal machines there is no friction. In this case a. W in = W out b. F in d in = F out d out 33. Apply the equation for mechanical advantage a. MA = F out / F in i. Mechanical advantage has no units! It is a ratio! 34. Apply the equation for efficiency a. % efficiency = (W out / W in ) x 100% i. % efficiency has no units! 35. Levers are a type of simple machine a. In a first-class lever the fulcrum is located between the input and output forces

4 b. In a second-class lever the output force is located between the input force and the fulcrum. c. In a third-class lever the input force is applied between the output force and the fulcrum. 36. Be able to describe the input and output forces, and the input and output distances the three classes of levers. a. For which one is the output force always greater than the input force? b. For which one is the output force always less than the input force? c. Give examples of each type of lever. 37. Apply the ideal mechanical advantage of a lever a. IMA = L in / L out 38. A pulley is a grooved wheel with a rope, chain, or cable running along the groove. a. Pulleys decrease the input force (how hard you have to pull) by distributing the output force among multiple strands of rope. The input force only has to be as large as the output force of one of the ropes. 39. A wheel and axle is a simple machine consisting of a shaft or axle attached to the center of a larger wheel, so that the wheel and axle rotate together. a. IMA = r w / r a 40. An inclined plane is a sloping surface, such as a ramp, that reduces the amount of force required to do work. a. IMA = l/h Chapter Describe the kinetic theory of matter a. How do molecules move i. In a solid? ii. In a liquid? iii. In a gas? iv. In plasma? 42. Temperature is a measure of the average kinetic energy of the particles in a substance a. The SI unit for temperature is Kelvin (K). b. Degrees Celsius = K c. Degrees F = 1.8 x degrees C Thermal energy is the sum of all potential and kinetic energies of all the particles in an object. a. A large block of ice has more thermal energy than a burning match 44. Heat is the thermal energy that flows from something at a higher temperature to something at a lower temperature. 45. Specific heat is the amount of thermal energy required to raise the temperature of 1kg of some material by 1 degree Celsius. 46. Use the following equation to calculate changes in thermal energy: a. Q = m(t f t i )C b. Q = change in thermal energy c. m = mass d. (t f t i ) = change in temperature

5 e. C = specific heat 47. Heat of fusion is the amount of energy required to change 1kg of a substance from a solid to a liquid 48. Heat of vaporization is the amount of energy required to change 1kg of a liquid into a gas. 49. A heating curve of a substance plots temperature as a function of energy added in Joules. The flat regions of the graph represent phase changes from solid to liquid, and liquid to gas. a. During phase changes, more energy can be added to a substance without its temperature increasing! b. To calculate the heat of fusion or the heat of vaporization i. Q = m (heat of fusion) ii. Q = m (heat of vaporization) 50. Phase changes a. Solids have a definite volume and shape b. Liquids have a definite volume only c. Gasses have no definite volume and no definite shape i. Gasses expand when heated. ii. Hot gasses are less dense iii. Cool gasses are more dense iv. The same is true of liquids, but to a much smaller extent 51. Transferring thermal energy a. Conduction is the transfer of thermal energy between colliding particles i. Insulation protects against the flow of energy by conduction ii. Metals are good conductors, and nonmetals and gasses are poor conductors b. Convection is the transfer of thermal energy by the movement of fluids (liquids and gasses) c. Radiation is the transfer of energy by electromagnetic waves. 52. Thermodynamics a. The first law states that the increase in thermal energy of a system equals the work done on the system plus the thermal energy transferred to the system. b. The second law states that for every event that happens in the universe energy becomes more dispersed. i. It is impossible for energy to flow from a cooler object into a warmer object unless work is done (think of a refrigerator). ii. A heat engine can never be made 100% efficient 53. Closed and open systems a. In a closed system nothing (no particles, no energy) gets in or out b. In a closed system thermal energy is constant c. In an open system thermal energy and increase or decreases. 54. Entropy is a measure of how spread out energy is. Based on the second law of thermodynamics, the entropy of the universe is always increasing. a. For an open system it is possible for entropy to decrease i. Life on earth is an example of decreasing entropy, where additional energy is constantly being added by the sun.

6 ii. If we think of the sun and earth together as a closed system, then entropy is still increasing because of the sun s depletion of its nuclear fuel.