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Lesson 5 concepts
| Question | Answer |
|---|---|
| Energy | the ability to cause change. Measured in Joules (J) |
| Kinetic energy | energy in motion |
| Formula for Kinetic Energy | KE = ½ mv2 |
| A jogger with a mass of 60 kg is moving at a speed of 3.0 m/s. What is the jogger’s kinetic energy? | KE=270 J |
| A baseball with a mass of 0.15 kg is moving at a speed of 40 m/s. What is the baseball’s kinetic energy? | KE=120 J |
| If a stone has 390 J of energy and is moving with a speed of 12 m/s, what is the mass of the stone? | m=5.42 kg |
| What is the velocity of a 0.06 kg ball moving with 75 J of energy? | v=50 m/s |
| 3 types of potential energy: | Elastic potential energy Chemical Potential energy Gravitational Potential Energy |
| Elastic Potential Energy | energy stored in objects being compressed or stretched |
| Chemical Potential Energy | energy stored in chemical bonds of compounds. |
| Gravitational Potential Energy: (GPE) | energy stored in objects that are above Earth’s surface. |
| GPE= what | HAM |
| How much gravitational potential energy does a 5 kg rock have if it is sitting on the edge of a cliff that is 10 m high? | GPE = 490 J |
| A Viking ship roller coaster at the fair has a mass of 36,000 kg. If at its peak it reaches a height of 20 m off the ground, how much gravitational potential energy does it have? | GPE = 7,056,000 J |
| A 1.5 kg apple pie is sitting on the kitchen counter. If it has 13.44 J of gravitational potential energy, how tall is the counter it sits on? | h = 0.914 m |
| A suitcase weighing 120 N sits on a counter 1.8 m high in the airport. How much energy does it have? | GPE = 216 J |
| Law of Conservation of Energy | energy can never be created or destroyed, it can only change forms. |
| Radiant energy | light that comes from the sun and lightbulbs; used to see and as a power source. |
| Thermal energy | heat that comes from fire, sun, etc.; used to heat objects |
| Electrical energy | comes from outlets and power plants; used to power electrical devices. |
| Sound energy | comes from a variety of sources; used most often for communication |
| Nuclear energy | comes from releasing energy from the nucleus of an atom; used in nuclear power plants. |
| Electromagnetic energy | form of energy that is reflected or emitted in the form of electrical and magnetic waves that can travel through space. |
| Mechanical energy | the total amount of kinetic and potential energy in a system. |
| Work | the transfer of energy that occurs when a force makes an object move. Measured in Joules |
| Two conditions must be met: | Object must move Force must be applied in the direction of the movement. |
| You move a 75 kg refrigerator 35 m. This requires a force of 90 N. How much work, in joules, was done while moving the refrigerator? | W = 3,150 J |
| A book weighing 1 N is lifted 2 m. How much work was done? | W= 2 J |
| A 1 kg book is lifted 2 m. How much work was done? | W = 19.6 J |
| 250 J of work are needed to push a box up a ramp. The force needed to push the box up the ramp is 10 N. How far up the ramp was the box pushed? | d = 25 m |
| If 56 J of work energy is required to lift a dumbbell to a height of 7 m, what is the weight of the dumbbell | w = 8 N |
| Power | the amount of work done in a certain time; the rate at which work is done. |
| It took 150 seconds to move a refrigerator. You did 3,150 joules of work in the process. How much power was required to move the refrigerator? | P = 21 J/s or 21 Watts |
| Machines | A machine is a device that changes the force or increases the motion from work. Machines make doing work easier! |
| Simple Machine | a machine that does work with only one type of movement. |
| There are 6 types of simple machines | Lever wheel and axle pulley inclined plane wedge screw |
| Compound Machine | a combination of two or more simple machines. ex: Scissors us two wedges and two levers |
| Efficiency | Machines can increase force OR increase speed but CANNOT increase force AND speed at the same time You always put more work into a machine than you get out! |
| Efficiency | is the ratio of output work to input work and is often measured in percent |
| You do 20 J of work in pushing a crate up a ramp. If the output work from an inclined plane is 11 J, then what is the efficiency of the inclined plane? | e = 55 % |
| Find the efficiency of a machine that does 800 J of work if the input work is 2,000 J. | e = 40 % |
| The input work on a pulley system is 75 J. If the pulley system is 84% efficient, then what is the output work from the pully system? | e = 63 J |
| Workers do 8,000 J of work on a 2,000 N crate to push it up a ramp. If the ramp is 2 m high, then what is the efficiency of the ramp? | W = 50%How are Machines Useful? |
| How are Machines Useful? | Change Direction of Force Increase Force Increase Speed |
| An ax has a wedge-shaped blade that changes the downward force you exert into outward forces that split the wood. | Change direction of Force |
| A carjack increases force but decreases speed- you move the handle faster than the car lifts | Increase Force |
| We can describe the effectiveness of a machine at increasing force by its | mechanical advantage |
| A crate weighs 950 N. If you can use a pulley system to lift that crate with a force of only 250 N, then what is the mechanical advantage of the pulley system? | MA = 3.8 |
| Calculate the mechanical advantage of a hammer if the input force is 125 N and the output force is 2,000N. | MA = 16 |
| Find the force needed to lift a 3,000 N weight using a machine with a mechanical advantage of 15. | Fin = 200 |
| Thermal energy | the sum of kinetic and potential energy of all the particles in an object |
| Temperature | measure of the average kinetic energy of particles in an object |
| Heat | the transfer of energy from one object to another |
| Transfer of Thermal Energy | there is no such thing as cold |
| Condcution | transfer of energy through matter by direct contact of particles |
| Convection | Transfer of energy through the movement of heated particles |
| Radiation | transfer of energy through electromagnetic waves occurs fastest in gasses |
| Conductors | materials that let heat flow easily |
| Insulators | materials that don't allows heat to flow easily |
| Specific Heat | the amount of heat ne=eded to raise the temperature of a 1 kg material by 1 degree cork |
| Formula for Thermal Energy | Q=MC/\T |
| A wooden block has a mass of 20 kg and a specific heat of 1700 J/kg degree Celsius. Find the change in thermal energy of the block as it warms from 15 degree Celsius to 25 degree Celsius | Q= 340,000 |
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