Physical Science EOCT Review

Physics – Energy, Force and Motion

To meet standards, students should be able to:

1)Identify the types, sources and uses of energy (chemical, thermal, mechanical, thermonuclear, photoelectric and electromagnetic)

2)Trace the transformation of energy within a given system

3)Relate molecular motion to the thermal energy changes in conduction, convection and radiation

4)Recognize the role ofconductors and insulators in the transfer of heat

5)Calculate the heat lost or gained by a system, given mass, specific heat capacity and temperature change

6)Using a phase diagram, explain the changes in matter within a system, as it relates to pressure and temperature

7)Calculate velocity of an object, given the displacement and time of measurement for that object

8)Calculate acceleration of an object, given the change in velocity and time for that object

9)Define inertia and recognize common examples of inertia

10)Measure and analyze the effects of balanced and unbalanced forces on an object in motion

11)Recognize the relationship between force mass and acceleration, as described in Newton’s second law

12)Solve application problems involving force, mass or acceleration of an object demonstrating an understanding of Newton’s second law

13)Calculate the force of an object, given the mass and the acceleration of that object

14)Recognize and determine the outcome of common examples of Newton’s third law

15)Identify common forces, including friction

16)Relate falling objects to gravitational force

17)Contrast mass and weight

18)Calculate the work and mechanical advantage of a simple machine

Thermal Energy

All forms of matter, whether a solid, liquid, or gas, are composed of atoms or molecules in constant motion. Because of this constant motion, all atoms have thermal (heat) energy. Whenever a substance is heated, the atoms move faster and faster. When a substance is cooled, the atoms move slower and slower. The "average motion" of the atoms that we sense is what we call temperature.

Temperature and heat ARE NOT technically the same thing. Temperature is the average motion of atoms and molecules. Heat is the energy that flows due to temperature differences. Heat is always transferred from warmer to cooler substances.

There are three ways to heat the atmosphere (or anything else, for that matter). These ways include conduction,convection, and radiation. How can you remember these? Let’s use an analogy to help you figure this out.

There are three ways to cook popcorn.

  1. Put oil in the bottom of a pan. Cover the bottom of the pan with popcorn kernels. Place the pan on the stove and turn on the burner to medium heat. Cover the pan with a lid. Periodically shake the pan so the kernels move around in the oil.
  2. Obtain a popcorn popper. Place the popcorn kernels in the popper. Plug in/turn on the popper. Hot air will transfer heat to the kernels, making them expand and pop.
  3. Microwave a bag of microwave popcorn.

Each of these methods of cooking popcorn is really an example of the three ways heat can be transferred.

  1. Conduction. This method of heat transfer is most familiar to people. If you have ever burned yourself on a hot pan because you touched it, you have experienced this first-hand. Conduction is heat transfer through matter. Metals conduct heat well. Air is not as good a conductor of heat. This is a direct contact type of heat transfer. The only air heated by the Earth is the air at the Earth’s surface. As a means of heat transfer, conduction is the least significant with regard to heating the Earth’s atmosphere. Which popcorn example does it relate to? #1. The heat is transferred by direct contact from the pan, to the oil, to the kernels of popcorn..
  2. Convection. Convection is heat transfer by the movement of mass from one place to another. It can take place only in liquids and gases. Heat gained by conduction or radiation from the sun is moved about the planet by convection. The radiation from the sun heats the air of the atmosphere, but the heating of the Earth is not even. This is because the amount of sunlight an area receives depends upon the time of day and the time of year. In general, regions near the equator have hotter air. This hot air rises, allowing cooler air to move in underneath the warm air. In our popcorn example this relates to #2. The hot air transfers the heat to the cooler kernels, and when enough hot air heats the kernels they pop.
  3. Radiation is the only way heat is transferred that can move through the relative emptiness of space. All other forms of heat transfer require motion of molecules like air or water to move heat. The majority of our energy arrives in the form of radiation from our Sun. Objects that are good absorbers of radiation are good radiators as well. The atmosphere, which does not absorb certain wavelengths of solar radiation, will absorb certain wavelengths of radiation. The particles that reach Earth from the Sun are within a wavelength that the Earth’s atmosphere will absorb. When the Sun heats the Earth, the Earth gets warmer in that location and re-radiates heat into the atmosphere, making it doubly warm. This relates to popcorn example #3. The kernels are heated by the radiation in the microwave, and the kernels heat up, giving off more heat to the kernels surrounding it and making it "doubly warm."

Conductors and Insulators

  • Heat passes through some materials easily and these materials are called thermal conductors.
  • Metals usually feel cold to the touch. Metals are good thermal conductors, because heat passes through them quickly.
  • Heat does not pass through some material such as plastic, oven glove, thermal underwear, cork board and wood. These materials are called thermal insulators.
  • These thermal insulators are good for keeping heat out as well and in. Some examples of good insulators are - a thermos - keeps hot things hot and keeps cold things cold, cooler - deeps the heat out and keeps the inside cool, and a polystyrene cup keeps the heat in and keeps it hot.
  • Remember that a good insulator is a poor conductor.
  • Heat loves to travel and will travel from a warmer material to a colder material. The heat will only travel from hot things to colder things and never the other way around.
  • Some materials allow heat to travel through easily and some don't. If you boil a tea pot on the stove, the pot becomes too hot to touch and whereas the tea pot handle does not get hot

Specific Heat Capacity

The specific heat capacity of a solid or liquid is defined as the heat required to raise unit mass of substance by one degree of temperature. This can be stated by the following equation:

where,
Q= Heat supplied to substance,
m= Mass of the substance,
c= Specific heat capacity,
T= Temperature rise.

Pressure vs Temperature (PTV)

Phase diagram, a graph that shows the relation between the solid, liquid, and gaseous states of a substance (states of matter) as a function of the temperature and pressure. The graph is divided into three regions, one for each of the physical states, and it specifies the range of temperatures at which the substance exists in each state for any value of the pressure.

Energy Transformations

Energy transformation is the process of changing energy from one form to another. This process is happening all the time, both in the world and within people. When people consume food, the body utilizes the chemicalenergy in the bonds of the food and transforms it into mechanical energy, a new form of chemical energy, or thermal energy.Energy transformation is an important concept in the application of the physical sciences. The ability for energy to be transformed automates, lights, entertains, and warms the world in an astounding multitude of ways.

The concept of energy transformation can be illustrated in a number of common activities. An engine, such as the engine in a car, converts the chemical energy of gas and oxygen into the mechanical energy of engine movement. A light bulb changes the chemical energy of the bulb into electromagnetic radiation, or light. Windmills harness the energy of the wind and convert it into mechanical energy in the movement of the turbine blades, which is then converted to electrical energy. Solar panels transform light to electricity.

Energy transformation can also be explained in terms of potential energy, the stored energy of a system, which can be converted into kinetic energy, the energy of movement. For example, a roller coaster sitting at the top of a hill is said to have potential energy. This potential energy is gravitational, which is gained when the coaster moves up the hill. Once the coaster begins to move down the hill, the force of gravity is exerted and the potential energy is transformed into the kinetic energy of the car moving. During energytransformations, potential energy is often transformed to kinetic energy and back again to potential energy.

During any kind of energy transformation, some energy is lost to the environment. As a result of this loss, no machine is ever 100% efficient. Commonly, a portion of the energy lost during energy transformation is lost as heat. This can be observed in practice by noting the heat emitted by a computer, a car, or another type of machine that has been in use for a period of time.

Kinetic Energy

The extra energy that an object possesses when it is in motion is known as kinetic energy. This motion of the object can be in any possible direction, and there are several different types of motion by which an object can move.

Mechanical Energy

Mechanical energy is the sum of energy in a mechanical system. This energy includes both kinetic energy, the energy of motion, and potential energy, the stored energy of position. A mechanical system is any group of objects that interact based on basic mechanical principles. The energy that a machine exerts is a type of mechanical energy.

Thermal Energy

Thermal energy or heat is another form of energy. It is a type of kinetic energy since it deals with the speed or velocity of the particles.

Electromagnetic Energy

The energy source required to transmit information (in the form of waves) from one place (material) to another. Some types of electromagnetic energy include: radio waves, microwaves, infrared waves, visible light, ultraviolet light, x-rays, and gamma rays. All electromagnetic forms of energy travel at the speed of light which is very fast.

Potential Energy

Potential energy is the stored energy of position. It can be thought of as energy that is “stored” by any physical system. It is called potential because, in its current form, it is not doing any work or causing any change in its surroundings. It does, however, have the potential to be converted to different forms of energy, such as kinetic energy.

Chemical Energy

Scientifically, energy is defined as the ability to do work. While there are many forms of energy, they can be grouped into two categories: potential energy, or stored energy; and kinetic energy, or energy of motion. Chemical energy is a form of potential energy and it is possessed by things such as food, fuels and batteries.

Gravitational Potential Energy

Gravitationalpotential energy is energy stored within an object due to its height above the surface of the Earth. In order for an object to be lifted vertically upwards, work must be done against the downward pull of gravity. The amount of energy used to lift the object against gravity is then stored as gravitationalpotentialenergy within the object. When the object is released and falls towards the Earth, the stored energy is converted into kinetic energy, the energy of movement.

Velocity and Acceleration

An object is in motion when it is continuously changing its position relative to a reference point and as observed by a person or detection device. For example, you can see that an automobile is moving with respect to the ground. The distance the object goes in a period of time is its speed. If the speed of an object is in a specific direction, it is called velocity. The change in velocity over a period of time is the acceleration of the object.

Speedis how fast an object is going with respect to an object. Velocity is a measure of the speed in a given direction. You can say the top speed of an airplane is 300 kilometers per hour (kph). But its velocity is 300 kph in a northeast direction.

In order to determine how fast an object is going, you measure the time it takes to cover a given distance, using the equation

d = vt where:d is the distance

v is the speed or velocity

t is the time covered

vt is v times t

From this equation, you can get the equation for velocity as v = d/t. Velocity (v) or speed equals the distance (d) traveled divided by the time (t) it takes to go that distance.

Example

For example, if a car went 120 miles in 2 hours, its average speed would be the distance of 120 miles divided by the time of 2 hours equaling 60 miles per hour (mph).

If it takes a car 2 minutes to travel 1 mile, its speed is 1 mile divided by 2 minutes, which equals 1/2 mile per minute or 30 miles per hour.

If you travel from Milwaukee to Chicago (90 miles) at an average velocity of 60 mph, it would take you 90 mi. ÷ 60 mph = 1.5 hours to travel the distance.

Acceleration

Acceleration is the increase of velocity over a period of time. Deceleration is the decrease of velocity. When you start running, you accelerate (increase your velocity) until you reach a constant speed.

Mathematically, acceleration is the change in velocity divided by the time for the change

a = (v2 − v1)/(t2 − t1)where:

  • v2 − v1 is the end velocity minus the beginning velocity
  • t2 − t1 is the measured time period between the two velocities

Often this is written as a = Δv/Δt, where Δ is the Greek letter delta and stands for difference.

For example, if an object speeds up from a velocity of 240 meters/second to 560 meters/second in a time period of 10 seconds, the acceleration is (560 - 240)/10 = 320/10 = 32 m/s/s or 32 m/s².

Changing direction can also cause acceleration (or deceleration) because the velocity in that direction has changed.

Newton’s Laws of Motion

Three Laws of Motion

  • Newton's First Law of Motion states that in order for the motion of an object to change, a force must act upon it, a concept generally called inertia.Inertia is the name for the tendency of an object in motion to remain in motion, or an object at rest to remain at rest, unless acted upon by a force.

The first law says that an object at resttends to stay at rest, and an object in motiontends to stay in motion, with the same direction and speed. Motion (or lack of motion) cannot change without an unbalanced force acting. If nothing is happening to you, and nothing does happen, you will never go anywhere. If you're going in a specific direction, unless something happens to you, you will always go in that direction. Forever.
You can see good examples of this idea when you see video footage of astronauts. Have you ever noticed that their tools float? They can just place them in space and they stay in one place. There is no interfering force to cause this situation to change. The same is true when they throw objects for the camera. Those objects move in a straight line. If they threw something when doing a spacewalk, that object would continue moving forever in the same direction and with the same speed unless interfered with by another force, such as another planet's gravity pulled on it.

  • Newton's Second Law of Motion defines the relationship between acceleration, force, and mass. As the mass goes up, the same force will cause an object to have less acceleration. This law is often stated mathematically as F= mass x acceleration.

The second law says that the accelerationof an object produced by a net (total) applied force is directly related to the magnitudeof the force, the same direction as the force, and inversely related to the mass of the object (inverse is a value that is one over another number... the inverse of 2 is 1/2). The second law shows that if you exert the same force on two objects of different mass, you will get different accelerations (changes in motion). The effect (acceleration) on the smaller mass will be greater (more noticeable). The effect of a 10 Newton force on a baseball would be much greater than that same force acting on a truck. The difference in effect (acceleration) is entirely due to the difference in their masses.

  • Newton's Third Law of Motion states that any time a force acts from one object to another, there is an equal force acting back on the original object. If you pull on a rope, therefore, the rope is pulling back on you as well.