1 Objective 4 Energy, Forces, and Motion Middle School Science Science STAAR Need to Know

2Science TAKS Need to Know Energy The ability to do work or to cause change

3Science TAKS Need to Know Chemical Energy – Energy transformations Chemical energy – when light energy from the sun is converted to the energy in the bonds of the sugar molecules formed in photosynthesis.

4Science TAKS Need to Know Chemical Energy Examples of chemical energy changing into heat energy: Lighting a match Burning a wood fire

5Science TAKS Need to Know Heat energy- Energy transformations Heat energy – energy is absorbed and temperature rises. Specific heat- the ability of a substance to absorb heat energy

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7 Electrical energy- Energy transformations Electrical energy- flow of electrons (a current) Other ways of generating electricity: Water flowing through a dam in a river to move turbines Wind generators that use the energy of moving wind & operate a generator Nuclear power plants convert atomic energy into heat. Heat boils water to form steam & then follows the same energy transformations as coal power plants

8Science TAKS Need to Know Many energy transformations… Electrical to mechanical: Electricity used to spin the CD (Spinning CD has mechanical energy due to its position or motion) Electrical to sound: A laser converts the digital information on the CD into electrical energy and this energy goes to the headphones as a vibration- this transmits Sound! Chemical to electrical: Batteries store chemical compounds that react when they are used to power something. This produces a flow of electrons which is electricity!!

9Science TAKS Need to Know Sound energy- Energy transformations Sound – consists of mechanical energy waves created by vibrations. Sound must travel through something (called “medium” or “media”) such as air, water, or a solid. The medium carries the energy of the wave from one place to another. Example: Air transmits the energy of the vibrating material in the headphones to your eardrums. A vacuum is a space that contains little or no matter. Sound can’t travel through a vacuum since there are no particles to squeeze together (compression) or spread apart (rarefaction)

10 Many times it takes a whole series of energy conversions to do a certain job. Many times it takes a whole series of energy conversions to do a certain job. For example, just to get the energy to make a piece of toast, there are several energy conversions involved. For example, just to get the energy to make a piece of toast, there are several energy conversions involved. Chemical energy stored in coal is released as heat and light energy when the coal is burned. The heat energy is used to produce steam and is changed into mechanical energy in a generator. The generator converts mechanical energy into electrical energy that travels through power lines into your home. When you use your toaster, that electrical energy is again changed into heat energy. Have you ever touched a light bulb when it was on? Or tried to change it when it burnt out after being on? What you have discovered is the conversion process of energy- When you turn on a light, not all of the electricity is converted to light energy. Some of the energy is converted to heat. Have you ever touched a light bulb when it was on? Or tried to change it when it burnt out after being on? What you have discovered is the conversion process of energy- When you turn on a light, not all of the electricity is converted to light energy. Some of the energy is converted to heat. Remember, energy is never lost- it’s only converted from one form to another. This is the law of conservation of energy This is the law of conservation of energy

11Science TAKS Need to Know Light waves do not need a medium to transmit energy! They can even travel through empty space.

12Science TAKS Need to Know Water waves are a form of a wave that transmits mechanical energy across the surface of water. A wave is a disturbance that transfers energy from one place to another.

13Science TAKS Need to Know Seismic waves are caused by earthquakes that transmit mechanical energy through the Earth’s layers.

14Science TAKS Need to Know Potential (PE) Stored energy

15Science TAKS Need to Know Before the yo-yo begins its fall it has stored energy due to its position. At the top it has its maximum potential energy. As it starts to fall the potential energy begins to be changed into kinetic energy. At the bottom its potential energy has been converted into kinetic energy so that it now has its maximum kinetic energy A waterfall has both potential and kinetic energy. The water at the top of Bridal Veil Falls has stored potential energy. When the water begins to fall, its potential energy is changed into kinetic energy. This change in energy also happens at Niagara Falls where it is used to provide electricity from the transformation of mechanical and electromagnetic energy.

16Science TAKS Need to Know Kinetic Energy (KE) Energy due to motion of an object Speed & mass affect kinetic energy– Faster/heavier…more Kinetic Energy Did you know that the gas burned in a car engine is chemical energy being turned into Kinetic Energy? Rubber band flying through the air has kinetic energy

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18Science TAKS Need to Know Energy Transformations Potential energy A rock sitting at the top of a cliff Roller coaster car at the top peak of a hill A swimmer posed to dive off the end of a diving board NO MOTION !! Kinetic energy A bouncing ball A moving roller coaster A track star running A girl skiing MOTION is the key!!!!

19Science TAKS Need to Know Forces may MOVE objects Forces may transfer energy between objects

20Science TAKS Need to Know You use force to move your body When you bend your arm, your muscles contract, which applies force to your arm bones. Your arm responds to this force by moving. During breathing, muscles contract (use force) to move air in and out of the lungs. The heart contracts (uses force) to pump blood through the blood vessels, carrying oxygen to the muscles.

21Science TAKS Need to Know All living things use force to move Emerging seedlings exert force on the surrounding soil. This force pushes the stem of the plant out of the ground. Plants exert force to open flower petals, curl & uncurl leaves & push roots through the soil. Force is used to move materials in & out of cells. Fish exert force to swim by pushing against the water.

22Science TAKS Need to Know In order for a force to move something, it must be an unbalanced force. This means that a force is stronger in one direction than the forces in the opposite direction.

23 Speed involves distance & time Average speed – can be calculated by dividing total distance by total time. S= D/T Instantaneous speed – an object’s speed at a specific moment When instantaneous speed does not change, an object is moving at constant speed; in this situation average speed and instantaneous speed are the same. Speed and direction of motion is velocity. Acceleration is the change in velocity divided by the time it takes for the change to happen. It can be a change in speed or a change in direction or both. Acceleration can be calculated using this formula: a = ( final speed - initial speed ) time

24 Acceleration can be shown on a speed-time graph. A change in speed is a change in velocity – so, a change in speed is an example of acceleration! Acceleration may be positive or negative. Negative acceleration is sometimes called deceleration.

25Science TAKS Need to Know Data can be displayed & interpreted in many ways

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27 The energy transferred when a force moves an object or changes its shape

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29 Newton’s 1 st law – states an object at rest will stay at rest unless acted on by an unbalanced force. An object in motion will stay in motion at the same speed and direction unless acted on by an unbalanced force.

30 - a moving object moves in a straight line with constant speed unless a force acts on it. - An object will not start moving unless a force acts on it - An object will not stop moving unless a force acts on it - An object will not change speed unless a force acts on it -An object will not change direction unless a force acts on it

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33 Acceleration can be calculated as Acceleration = force/mass ~or~ Force = mass X acceleration The more mass an object has the more force it takes to cause acceleration. - Big masses are hard to accelerate. - Small masses are easy to accelerate. - Objects accelerate more quickly when a greater force is used. 2 nd law states that the acceleration of an object depends on its mass and the size and direction of the force acting on it.

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