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3. Motion – ENERGY All life depends upon energy which allows us to move and interact with our environment. Formally energy is defined as the ability or capacity to do work. Most of the energy on the earth comes from the sun. All energy originates from four fundamental forces: strong nuclear forces, weak nuclear forces, gravitational forces, and electromagnetic forces. We find that these fundamental forces act to produce common forms of energy in our environment. These forms include: thermal, light, sound, mechanical, electrical, chemical, and nuclear. The various forms of energy can be indicated by two types, potential and kinetic energy. They are described by the amount of stored (potential) and/or dynamic (kinetic) energy they possess. Potential Energy is the energy stored by an object as a result of its position or the position of its parts. A rock on a table, a bowl of cereal, a stick of dynamite, and a tank of gasoline are all examples of objects that have energy stored in atoms or molecules. The rock has potential energy because of its height that can be released and converted to kinetic energy and heat, if it is dropped. Potential energy is equal to force (newtons) multiplied by distance. (meters).The units of measurement is newton-meters and is referred to as a joule (1 newton-meter = 1 joule). Remembering that f=m x a where f = force, m= mass and d= distance. In this investigation the d will be the height (h) which the truck drops and a is due to gravity (g) then f=m x g. This relationship is often written P.E. = mgh Potential Energy = mass x acceleration of gravity x height Where: m = g = h = or P.E. = m x g x h the mass of the object measured in kilograms. the acceleration of gravity, on planet Earth, 9.8 meters / second2. height in meters that the object falls measured in meters. For Example: When m = 378 Kg, g= 9.8 m/sec2 and h = 200 m P.E. = mgh P.E. = 378 kg x 9.8 m/sec2 x 200 m Note: 1 kilogram- meter / sec2 is 1 newton which is 1 joule. P.E. = 740,880 N-m or 740,880 joules Kinetic Energy is the dynamic energy that matter has because of its motion and mass. Examples of kinetic energy are: moving car, a falling rock, a bullet shot from a gun or a flow of electrons. The unit of measurement is labeled newton-meters. 1 newton-meter is 1 joule. Kinetic Energy = 1/2 mass x velocity2 or Where: m = v = K.E. = 1/2 m x v2 the mass of the object moved is measured in Kilograms. the velocity measured in meters per second. For Example: When m = 1000 kg and v 38.5 m/s K.E. = 1/2 x m x v2 K.E. = 1/2 x 1000 kg x (38.5m/s x 38.5m/s) K.E. = 1/2 x 1482300 kg-m2/s2 K.E. = 741,125 kg-m2/s2 = 741,125 newton-meter = 741,125 joules Energy Track Thickness = 0.0075-m 0.3800-m 0.4000 -m 1. Does Energy Depend On Height (Force)? a. In this experiment we will keep the timed distance, mass of the truck, support block position and starting position constant while varying the height of the support block which will change the force on the truck. b. Obtain the force exerted by the truck due to the height by watching the video laboratory. c. Obtain the times for the three trials for each height by watching the video laboratory. d. Calculate the average time, velocity, potential and kinetic energy. Formulas are provided. Time Trials Block Height (meters) Height of Truck (h) (meters) Force on Truck (Newton) Trial 1 Trial 2 Trial 3 (seconds) (seconds) (seconds) Speed Average Time (seconds) V=d/t (m / sec) Energy Potential P.E.= mgh K.E.= ½ mv2 Kinetic (Joules) (Joules) 0.0300 0.0600 0.0900 e. f. g. h. Does the change in height (force) on the truck effect time and energy, explain? Explain why potential energy and kinetic energy are not numerically equal. Does the change in height (force) on the truck effect time and energy, explain? _____ Explain why P.E. and K.E. are not equal. _____ 2. Does Energy Depend On Mass? a. In this experiment we will keep the timed distance, support block height, support block position and starting position constant while varying the mass of the truck. b. Obtain the force exerted by the truck due to the mass by watching the video laboratory. c. Obtain the times for the three trials for each mass by watching the video laboratory. d. Calculate the average time, velocity, potential and kinetic energy. Formulas are provided. Time Trials Mass of Truck (Kg) Force on Truck (newton) Height of Truck (h) (meters) 0.0600 0.0375 0.1200 0.0375 0.1800 0.0375 0.2400 0.0375 Trial Speed Trial Trial 1 2 3 Average Time (sec.) (sec.) (sec.) (seconds) V=d/t (m / sec) Energy Potential P.E.= mgh (joules) Kinetic K.E.= ½ mv2 (joules) e. Does the change in mass affect time and energy? f. Explain why potential energy and kinetic energy are not the same. g. How does the change in mass affect velocity and energy? h. Explain why P.E. and K.E. are not equal. 3. Efficiency Since potential energy is the total theoretical energy and the kinetic was the actual energy one could determine the efficiency. Do this for truck without added mass. % efficiency = (potential energy − kinetic energy) potential energy * 100