EnergyWork &Click Here To Start

Dr. Merced GutierrezSubmitted To:

Work & Energy

Sultiz, Larry J.

Group 1

Leader:

Members:

Cheryl Mae O. Mabuting Dianara M. PalermoApril Rose C. Torrejas Regine L. Lacaza

Work

Sultiz, Larry J.

WorkIn physics, work representsa measurable change in asystem, caused by a force.

If you push a box with a force of one newton for a distance of one meter, you have done exactly one joule

of work.

Work

Work(force is parallel to distance)

W = F x dDistance (m)

Force (N)

Work (joules)

Example 1:

I am holding a 2 kg block of cheese inmy hands. I walk 12 m to the other sideof the room.

Explain if I did any work.

Example 2:

I decide to do a little weight lifting(but I’m going to start off slow!). I lift10 kg from the floor, over my head, andback down to the floor.

Explain if I did any work.

Example 3:

Last winter my car got caught in a snowbank. I promise one of my friends that ifhe comes over to do some work for me I’llbuy him pizza. We get behind the car andpush it out of the snow.

Explain if I did any work.

Example 4:

I am holding a 10kg book in my hand. I put it down on the floor. Explain if we did any work.

Explain if I did any work.

Example 5:

My nephew Lanz Gabriel, grabs myother nephew Zendric’s leg and drags him2.3 m across the floor. If he exerted aforce of 8.1 N to do this, determine howmuch work he did?

Explain if I did any work.

Work(force at angle to distance)

W = Fd cos (q)

Distance (m)

Force (N)

Work (joules) Angle

Example 6:If you were pulling a box, which moves 12.7 m whenyou pull along the rope with a force of 76.0 N withan angle of 300, determine how much work you did.

Why the path doesn't matter

Work(done against gravity)

W = mghHeight object raised (m)

Gravity (m/sec2)

Work (joules)

Mass (g)

Calculate work

• A crane lifts a steel beam with amass of 1,500 kg.

• Calculate how much work is doneagainst gravity if the beam islifted 50 meters in the air.

Energy

April Rose C. Torrejas

What is Energy?

Energy is the ability to do work.

If an object or organism does work (exerts a forceover a distance to move an object) the object ororganism uses energy.

Because of the direct connection between energy andwork, energy is measured in the same unit as work:joules (J).

Forms of EnergyThe five main forms of energy are:

1.Heat2.Chemical3.Electromagnetic4.Nuclear5.Mechanical

Heat Energy

The internal motion of the atoms is called heat energy, because moving particles produce heat.Can be produced by friction.Causes changes in temperature and phase

of any form of matter.

Forms of Energy

Chemical Energy

Is required to bond atoms togetherand when bonds are broken, energy isreleased.

Forms of Energy

Electromagnetic Energy

Power lines carry electromagnetic energyinto your home in the form of electricity. Light is a form of electromagnetic energy. Each color of light (RoyGBiv) represents a

different amount of electromagnetic energy.Electromagnetic Energy is also carried by X-rays, radio waves, and laser light.

Forms of Energy

Nuclear Energy

The nucleus of an atom is the source ofnuclear energy.The sun’s energy is produced from a

nuclear fusion reaction in which hydrogennuclei fuse to form helium nuclei.

Forms of Energy

Mechanical Energy

When work is done to an object, it acquiresenergy. The energy it acquires is known asmechanical energy.When you kick a football, you give mechanical

energy to the football to make it move.

Regine L. Lacaza

Potential Energy

When the work is waiting to be done, or when there is the potential for work to be performed, we term the energy “potential”

The unit for potential energy is: Joules or kg/m2/s2

Potential Energy

Ep = mgh Height (m)

Mass (kg)

Potential Energy(joules)

Accelerationof gravity (m/sec2)

Gravitational Potential Energy (GPE)- associated with an object at a given location above the surface of the earth.

Potential EnergyA cart with a mass of 102 kg is pushed

up a ramp.

The top of the ramp is 4 meters higher than the bottom.

How much potential energy is gained by the cart?

Calculate the gravitational potential energy of askydiver with a mass of 80kg about to jump out of a planeat an altitude of 5000m?

PE = m x g x hPE = 80 x 9.8 x 5000 [remember acceleration due to gravity = 9.8 m/s2

PE = 3920000 Joules = 3920 kilo joules (kJ)

A brick with a mass of 1 kg is lifted to the topof a 4 m high roof. It slips off the roof and falls tothe ground.Calculate the gravitational potential energy of thebrick at the top of the roof and on the ground onceit has fallen.

The mass of the brick is m = 1 kgThe height lifted is h = 4 m

a. We are asked to find the gain in potential energyof the brick as it is lifted onto the roof?

Ep= mgh=(1kg)(9.8m/𝑠2)(4m)=39.2 J

A boy has a mass of 30 kg climbs onto the roof of agarage. The roof is 2.5 m from the ground.

1.How much potential energy did the boy gain by climbing onto the roof?

PE= mghPE= (30)(9.8)(2.5)

PE= 735 J

The boy now jumps down. What is the potential energy of the boy when he is 1 m from the ground?

PE= mgh= (30kg)(9.8m/𝑠2)(1m)=294 J

When he is on the ground the height is 0 and so the potential energy is 0J.

Elastic Potential Energy

- can be thought of as the energy stored in the deformed spring (one that is either compressed or stretched from its equilibrium position).

Equation for EPE = 1

2kx2

Example:

50N of force is applied to a spring having 150N/m springconstant. Find the amount of compression of the spring.

Fspring = -kx=Fapplied50N = - 150.x

X = -3m “-“shows the direction of compression.

The vertical spring is attached to the load of mass 5 kg and is compressed by 8 m. Calculate the Force constant of the spring?

Solution:Given: Mass m = 5kg,

Distance x = 8 cm,Force Constant k = ?

Force is given by F = ma= 5 kg × 9.8 m/s2

= 49 N.Force in the stretched spring is given by F = kxForce Constant k = Fx

= 49N8m= 6.125 N/m.

An Olympic archer applies a force of 100N in pulling back her bow by 0.5m. How much energy is stored in the bow?

Elastic PE = F x dElastic PE = 100 x 0.5Elastic PE = 50 Joules

Thus 50 Joules of work was done by the archer on the bow which will be transferred to the arrow when it is released.

Kinetic Energy

Cheryl Mae O. Mabuting

Kinetic Energy

The work done on a body that caused thebody to be set in motion with somespeed v can be expressed as function of thebody's final speed v and mass m, independentof type of force that acted on the body.

Kinetic Energy

Kinetic energy is a scalar. An energy in motion. The kinetic energy of an object is completely

described by magnitude alone. The units are the same as for work (i.e.

Joules, J).

Kinetic Energy

Ek = 1 mv2

2

Speed (m/sec)

Mass (kg)

Kinetic Energy

(joules)

Kinetic Energy

The kinetic energy of a moving object depends on two things: mass and speed.

Kinetic energy is proportional to mass.

Mathematically, kinetic energy increases as the squareof speed.

If the speed of an object doubles, its kinetic energy increases four times. (mass is constant)

Kinetic Energy

Calculate Kinetic Energy

A car with a mass of 1,300 kg is going straight ahead at a speed of

30 m/sec (67 mph).

Calculate:

a) The kinetic energy of the car.

1.

2.

Note the following:

1. Both balls had potential energy as they rested on the table.2. By resting up on a high table, they also had gravitational energy..3. By moving and falling off the table (movement), potential and gravitational energy changed to Kinetic Energy. Can you guess which of the balls had more kinetic energy? (The big and heavier ball)

Some illustrations of kinetic energy

Some illustrations on kinetic energy

CALCULATIONS:

A 500 kilogram car is driving at 15 meters/second. What's its kinetic energy?

Solution:V= 15m/s M= 500kgKinetic energy = 1/2mv2(500kg)(15m/s2

KE = 56250 Joules

CALCULATIONS:

Determine the kinetic energy of a 625-kg roller coaster car that is moving with a speed of 18.3 m/s.

Solution:KE = 0.5*m*v2

KE = (0.5) * (625 kg) * (18.3 m/s)2

KE = 1.05 x105 Joules

WORK-ENERGY THEOREM

The energy associated with the work done by the net force does not disappear after the net force is removed (or becomes zero), it is transformed into the Kinetic Energy of the body. We call this the Work-Energy Theorem.

KE= ½ mv2

Wnet = ∆ KEWnet = KEf – KEi

Relation bewteen KE and W:

The work done on an object by a net force equals the change in kinetic energy of the object:

W = KEf - KEi.

This relationship is called work-energy theorem

Potential Energy Kinetic Energy

DefinitionPotential energy is due do position, composition or

arrangement.Kinetic energy is energy due to motion.

Formulamass of the object x acceleration of Gravity x Height of

the object, PE = m x g x h

1/2 x mass of the object x speed of the object², KE = ½ x

M x V².

S.I. Unit Joule Joule

Example Wound up spring of a toy, a stone on top of a hill, etc. A person who is walking, a pen falling from a table, etc.

Types Gravitational, Elastic and Chemical Potential Energy. Rotational and Translational Kinetic Energy.

CONSERVATIVEAND

NON-CONSERVATIVEFORCES

Dianara M. Palermo

CONSERVATIVE FORCES

Forces that store energy.

The work a conservative force does on an object in moving it from A to B is path independent - it depends only on the end points of the motion.

Can be thought of as a force that conservesmechanical energy.

KE(final) + GPE(final) = KE(initial) + GPE(initial)

Example:

Gravitational force: mechanical work againstit depends just on difference in elevation nothow an object is lifted.

Elastic force: work against spring only depends onlength change.

Paths for moving a

particle from point A to point B

NON-CONSERVATIVE FORCE

a force that goes against any kind offriction because of the energy it takes fromthe system can't be stored.

The work done by a non conservative forcedoes depend upon the path taken.

Example:

Law of Conservation of Energy

As energy takes different forms and changes things by doing work, nature keeps perfect track of the total.

No new energy is created and no existing energy is destroyed.

Thank YouFor Your

Cooperation!