Energy Chapter 4
The nature of energy • Energy: The ability to do work or cause change • All energy involves either motion or position • Where are we using energy right now?
What are some types of energy? Thermal energy : The total kinetic energy of particles that make up an object Chemical energy: The energy of a compound changes as the atoms are rearranged to form new compounds. Electrical energy: the energy of moving electrons Sound energy: The energy of vibration Light energy: The energy of vibration of electrically charged particles Nuclear energy: the energy associated with changes in the nucleus of an atom
Mechanical NRG • Mechanical energy is the total amount of potential and kinetic energy in a system
Kinetic energy • Kinetic energy is energy in the form of motion.
How to calculate kinetic energy: • Kinetic energy = ½ (mass x velocity 2) or • KE = ½ (mv2) • Labeled as Joules • Joule is expressed in N x m or • 1 Joule= 1 kg * (m/s)2 • What is the kinetic energy of a 45 kg object moving at 13 m/sec? • mass = 45 kg velocity = 13 m/sec • KE = ½ (mv2) • So… KE = 1/2 (45 kg)(13 m/sec)2 • Solving the equation gives a kinetic energy value of 3802.5 J
Calculate • Determine the kinetic energy of a 1000-kg roller coaster car that is moving with a speed of 20.0 m/s. • KE = (0.5) * (1000 kg) * (20 m/s)2 • KE = 200 000 Joules • If the roller coaster car in the above problem were moving with twice the speed, then what would be its new kinetic energy? • KE = 0.5*1000 kg*(40 m/s)2 • KE = 800 000 Joules • As your speed doubles your kinetic energy quadruples.
Gravitational Potential Energy • Grav. Potential energy = weight x height • Or….. • PE = w x h • Elastic Potential energy: energy stored by compressing or stretching something • A 37 N object is lifted to a height of 3 meters. What is the potential energy of this object? • weight = 37 N height = 3 meters • Solving the problem gives a potential energy value of 111 J.