Machines, Work and Energy

How does one generate thermal energy?

when a machine is used, some of the input energy changes to thermal energy due to friction.

Work Calculation

work in joules = applied force (in newtons) x distance (in meters) or W=Fd

Potential Energy

Energy that is stored and held in readiness

AMA

Actual mechanical advantage of a machine. They do not have as high of a mechanical advantage as ideal machine because some of the effort is lost in overcoming friction. EQUATION......AMA=fout/fin ama = force out/force in

Why are machines inherently inefficient, and what does that mean in terms of work in vs. work out?

Ideal machine: work in, work in, work out actual machine: work in, work out, work out

Nature of Energy

It is the ability to cause change, ability to do work

What factors affect the amount of potential energy that an object has?

Stored energy, elastic, chemical, and gravitational are factors that can affect the amount of potential energy an object has. potential energy is energy that hasn't happened yet. It is the energy that could be created by movement. It is the energy an object has the potential to create. The energy produced is determined similarly to kinetic. It depends on the object's mass, the gravitational pull when up or down slopes, and the height of the reference point.

What are the different families of machines and how are the machines related?

A lever is a bar that is free to pivot about a fixed point called a fulcrum. A pulley is a grooved wheel with a rope running along the groove. A wheel and axle consists of two different-sized wheels that rotate together. An inclined plane is a sloping surface used to raise objects. The screw and the wedge are special types of inclined planes. A combination of two or more simple machines is called a compound machine.

Efficiency and Incidental Work

A machine multiples force. How effective the machine is in that is called efficiency. Efficiency is expressed as a percentage. Efficiency can be determined by the following equation. The efficiency of a machine is the output work divided by the input work times 100 efficiency= Work out/Work in X 100%

Where does the energy that we use come from?

Energy is always transferred from the object that is doing the work to the object on which the work is done. Remember that energy is always conserved. When you do work on a machine, you transfer energy to the machine. When the machine does work on an object, energy is transferred from the machine to the object. Because energy cannot be created or destroyed, the amount of energy the machine transfers to the object cannot be greater than the amount of energy you transfer to the machine. A machine cannot create energy, so Wout is never greater than Win. However, the machine does not transfer all of the energy it receives to the object. In fact, when a machine is used, some of the input energy changes to thermal energy due to friction. The energy that changes to thermal energy cannot be used to do work, so Wout is always smaller than Win.

What is energy?

Energy is the ability to do work. Energy is also the ability to cause change. When work is done, energy moves from one place to another or changes from one form to another. Examples: turn on electric light turns dark room brighter, turn on CD Player and sound is played. Energy can be in different forms: electrical, chemical, radiant, and thermal

What factors affect the amount of kinetic energy an object has?

Factors that affect the kinetic energy of an object: objects mass and speed. Kinetic energy is energy in motion. kinetic energy is the energy produced by movement. Kinetic energy is the energy an object produces when moving. Due to gravity, kinetic energy is affected by the object's mass and velocity

How does one do work?

First, Applied force must make the object move then 2nd, the object must move in the direction of the applied force.

IMA

Ideal Mechanical Advantage. A simple machine would be considered ideal if it had no friction. The mechanical advantage of a machine without friction is called the ideal mechanical advantage, or IMA. EQUATION.......IMA= din/dout IMA = distance input/distance out The IMA can be calculated by dividing the input distance by the output distance. For a real machine, the IMA would be the mechanical advantage of the machine if there were no friction.

How could an object's kinetic energy be transformed into potential energy? Vice Versa? (object's potential energy into kinetic energy?)

Kinetic to Potential: As a battered ball speeds up or slows down, its kinetic and potential energy are always changing. The amount of mechanical energy always stays the same. The kinetic and potential energy continually change form back and forth, and no energy is destroyed. Potential to Kinetic: If a boulder was on the tip of a cliff, the wind could move it ever so slightly so that it could come crashing down. The boulder's energy is potential until it is moved so that it rolls down the hill. Then it is kinetic. It is affected by both factors of kinetic and potential energy.

What if there is no motion in the direction of the applied force?

No work will be done then

Inputs and Outputs

Remember that work is calculated by multiplying force by distance. The input work is the product of the input force and the distance over which the input force is exerted. The output work is the product of the output force and the distance over which that force is exerted.

How are each class of lever set up and what are some examples of each

There are three classes of levers. The differences among the three classes of levers depend on the locations of the fulcrum, the input force, and the output force. The screwdriver is being used as a first-class lever. The fulcrum is the paint can rim. (Screwdriver is taking off lid) The screwdriver used to open the paint can in Figure 14A is an example of a first class lever. For a first-class lever, the fulcrum is located between the input and output forces. The output force is always in the opposite direction to the input force in a first-class lever. A wheelbarrow is a second-class lever. The fulcrum is the wheel. For a second-class lever, the output force is located between the input force and the fulcrum. Look at the wheelbarrow in Figure 14B. The girl applies an upward input force on the handles, and the wheel is the fulcrum. The output force is exerted between the input force and the fulcrum. For a second-class lever, the output force is always greater than the input force. A baseball bat is a third-class lever. The fulcrum here is the batter's left hand. Many pieces of sports equipment, such as a baseball bat, are third-class levers. For a third-class lever, the input force is applied between the output force and the fulcrum. The right-handed batter applies the input force with the right hand, and the left hand is the fulcrum. The output force is exerted by the bat above the right hand. The output force is always less than the input force in a third-class lever. Instead, the distance over which the output force is applied is increased.

How do you find the inputs/outputs to each type of machine?

Two forces are involved when a machine is used to do work. You exert a force on the machine, such as a bottle opener, and the machine then exerts a force on the object you are trying to move, such as a bottle cap. The force that is applied to the machine is called the input force. F in stands for the input force. The force applied by the machine is called the output force, symbolized by F out. When you try to pull a nail out of wood with a hammer, as in Figure 10, you apply the input force on the handle. The output force is the force the claw applies to the nail.

Why do we use machines?

We use machines to reduce the amount of effort or work we exert, and also to increase our ability to lift or move objects. To do work with less force and multiply forces or change direction of forces

What is the relationship between work and energy?

When work is done, a transfer of energy always occurs. Work is done on an object when a force is exerted on the object and it moves in the direction of the force. • If a force, F, is exerted on an object while the object moves a distance, d, in the direction of the force, the work done is W=Fd • When work is done on an object, energy is transferred to the object. This is easier to understand when you think about carrying a heavy box up a flight of stairs. Remember that when the height of an object above Earth's surface increases, the gravitational potential energy of the object increases. As you move up the stairs, you increase the height of the box above Earth's surface. This causes the gravitational potential energy of the box to increase. You may recall that energy is the ability to cause change. If something has energy, it can transfer energy to another object by doing work on that object. When you do work on an object, you increase its energy. The student carrying the box transfers chemical energy in his muscles to the box. Energy is always transferred from the object that is doing the work to the object on which the work is done

Work Formula

Work = Force X Distance *The unit of force is newtons *The unit of distance is meters *The unit of work is newton-meters *One newton-meter is equal to one joule *So, the unit of work is a joule

What factors affect the amount of power in a situation?

Work and Time Calculating Power: it is the rate at which work is done. To calculate power, divide the work done by the time that is required to do the work. Power Equation power (in watts) = work (in joules)/time (in seconds) P = W/t The SI unit for power is the watt (W). One watt equals one joule of work done in one second. Because the watt is a small unit, power often is expressed in kilowatts. One kilowatt (kW) equals 1,000 W.

Why can't a second hill on a rollercoaster, or the second bounce of a ball be as high as the first?

because it doesn't have as much potential energy left

What are the ways that machines can change a force?

by changing the applied force, changing the distance over which the force is applied, and by changing the direction of the applied force.

Simple Machines

is a machine that does work with only one movement of the machine. There are six types of simple machines: lever, pulley, wheel and axle, inclined plane, screw, and wedge. The pulley and the wheel and axle are modified levers, and the screw and the wedge are modified inclined planes OTHER EXAMPLES: KNIVES, SCISSORS, AND DOORKNOBS

Power

is the amount of work done in one second. It is a rate, the rate at which work is done. Calculating Power: it is the rate at which work is done. To calculate power, divide the work done by the time that is required to do the work. Power Equation power (in watts) = work (in joules)/time (in seconds) P = W/t The SI unit for power is the watt (W). One watt equals one joule of work done in one second. Because the watt is a small unit, power often is expressed in kilowatts. One kilowatt (kW) equals 1,000 W. When energy is transferred, power can be calculated from the equation P = E/t

Work and energy relationship

is the energy transferred when a force makes an object move. Energy is the ability to cause change and the ability to do work. One object can transfer energy to the 2nd object. When work is done, energy is transferred from one object to another. If you push against the desk and it doesn't move, then you haven't done any work on the desk. Doing Work : There are two conditions that have to be satisfied for a force to do work on an object. One is that the applied force must make the object move, and the other is that the movement must be in the same direction as the applied force.

What role does friction play in using machines?

it converts some energy into thermal energy: For real machines, some of the energy put into a machine is always converted to thermal energy by frictional forces. For this reason, the output work of a machine is always less than the work put into the machine. However, the machine does not transfer all of the energy it receives to the object. In fact, when a machine is used, some of the input energy changes to thermal energy due to friction. The energy that changes to thermal energy cannot be used to do work, so Wout is always smaller than Win.

Types of Machines

simple machines and compound machines simple machine • lever • pulley • wheel and axle • inclined plane • screw • wedge • compound machine: (A combination of two or more simple machines): Car, can opener

How does the law of conservation of energy apply to the transformations we demonstrated in class?

that there can't be energy created or destroyed

Kinetic Energy

the energy an object has due to its motion

Conservation of Energy

the law that states that energy cannot be created or destroyed but can be changed from one form to another

Work and Machines

• Machines make doing work easier by changing the applied force, changing the distance over which the force is applied, or changing the direction of the applied force. • Because energy cannot be created or destroyed, the output work cannot be greater than the input work. • In a real machine, some of the input work is converted into heat by friction. Machines can make work easier by increasing the force that can be applied to an object. A screwdriver increases the force you apply to a screw. A second way that machines can make work easier is by increasing the distance over which a force can be applied. A leaf rake is an example of this type of machine. Machines also can make work easier by changing the direction of an applied force. A simple pulley changes a downward force to an upward force.