Understanding Hydraulic System

A hydraulic system operates based on Pascal's principle.

In this hydraulic system, a small force, F1 is applied to the small piston resulting in a large force , F2 at the piston K. The pressure, due to the force, F1, is transmitted by the liquid to the large piston.

Pressure, P = F1/A1

This pressure is transmitted through the liquid and acts on the base of the large piston.

Force on the large piston, F2 = P X A2 = (F1/A1) X A2.

The large force causes the load to rise.

Also F2/F1 = A2/A1

Output force / input force = output piston area / input piston area

Because of the much larger surface area, A2 of the piston K compared to the surface area, A1 of the piston, the resultant force, F1.


This shows that a large force can be produced by a small force, using Pascal's principle.

Hydraulic systems act as a force multiplier where A2/A1 is the multiplying factor.

For example, if A2=5A1, then F2 = 5F1

since F2 = F1 X (A2/A1)

A hydraulic system must not contain any air bubbles in any portion of its hydraulic fluid system.
The presence of air bubbles in the hydraulic fluid system will reduce the efficiency of the system as part of the applied force will be used to compress the air bubbles.

Understanding Displacement, Speed and Acceleration

Distance and Displacement

Distance is the total path length traveled from one location to another. It is a scalar quantity.

Displacement is the distance between two locations measured along the shortest path connecting them, in specified location. It is a vector quantity. The SI unit of distance and displacement is metre (m).


Speed and Velocity

Speed is the distance traveled per unit time or the rate of change of distance.

Speed = total distance traveled / time taken

Velocity is the speed in a given direction or the rate of change of displacement.

Average velocity = displacement/ time taken


Acceleration and Deceleration

Acceleration is the rate of change of velocity.

Acceleration = change of velocity / time taken

Change of velocity = final velocity (v) – initial velocity (u)

Acceleration = (final velocity – initial velocity) / time taken = (v – u) / t


Things to remember:

1. Constant velocity means the object is not accelerating. Acceleration is zero.

2. Constant acceleration means the object is increasing its velocity.

Understanding Work and Energy

Work
1. Work is defined as the product of the applied force and the displacement of an object in the direction of the applied force.
2. W = F x d
3. W= work done, F = force applied, d = displacement in the direction of force.
4. SI unit for work = Joule (J), other unit = Nm
5. Work is not done when:

• The object is stationary or not moving
• No force is applied on the object in the direction of displacement.
• The direction of motion of the object is perpendicular to that of the applied force.

6. When work is done to an object, energy is transferred to the object.


Energy (Energy is the capacity to do work)
1. Energy exists in different forms: kinetic energy, gravitational potential energy, elastic potential energy, sound energy, heat energy, light energy, electrical energy and chemical energy.
2. The unit for energy is Joule (J) – same as work
3. The work done is equal to the amount of energy transferred.
4. Kinetic energy is the energy of an object due to its motion.
5. Kinetic energy or work done is given by:

• a. ½ mv²
• b. M = mass, v = velocity
• c. Unit: Joule

6. Gravitational potential energy is the energy of an object due to its higher position in the gravitational field.

• E = mgh
• M = mass, g = acceleration due to gravity, h = height in metre

Understanding Scalar and Vector quantities

Scalar quantities: Quantities that have magnitude only. ( Speed, mass, distance)

Example:

For example speed has unit of ms^-1. but it has no direction.

Mass is kg but we don't know the direction.

Distance is 2km but no direction.

Vector quantities: Quantities that have magnitude and direction. (Velocity, Weight, Displacement)

Example:

Velocity unit is ms^-1 but we must state the direction that is whether from right to left.

Weight unit is Kg but the direction is towards the gravity pull of the earth.

Displacement is 2km but to the north from the point of reference.

Understanding Measurement

A micro balance is used to measure minute masses. It is sensitive but not very accurate.


Slide callipers are usually used to measure the internal or external diameter of an object.


A micrometer screw gauge is used to measure the diameter of a wire of the thickness of a thin object.

All measurement must consider this:

Accuracy: Ability of the instrument to measure the true value or close to the true value. The smaller the percentage error, the more accurate the instrument is.

Sensitivity of an instrument is the ability of the instrument to detect any small change in a measurement.

Consistency: ability of the instrument to produce consistent measurement.(the values are near to each other). The lower the relative deviation, the more consistent the measurement is.

How to increase accuracy?
- repeat the measurements and get the mean value.
- correcting for zero error.
- avoiding parallax error.
- use magnifying glass to aid in reading.

The sensitivity of a mercury thermometer can be increased by;
-having a bulb of thinner wall.
-having a capillary tube of smaller diameter or bore.

Understanding Pressure

1. Pressure on an area, A is the normal force, F, whish is being applied perpendicularly to the area.
2. Pressure on an area, A is expressed as the normal force, F per unit area, A.
3. P = (F/A)
4. This SI unit for pressure is the pascal, Pa, where 1 Pa = 1 N/m2 (metre square).
5. Pressure is increased: if the force, F applied to a given area, A is increased and if a given force, F is applied to a smaller area, A.
6. If a balloon is pressed against by a finger, the balloon will only change its shape a bit. If the balloon is pushed against by a needle with the same force, the balloon will burst. This is because a finger has a larger surface area (A) than a needle. Hence, the needle exerts much pressure than the finger and perforates through the surface of the balloon and making a hole and freeing the air inside the balloon.

The Importance of Speed and Velocity in sports.

The Best Explanation from Grade 7 students

==========================================================

Written by : Brigitta, Kevin Dwi, Raissa [7a]

Speed and velocity is very important and need to be included in sports. They have many useful benefits that many people need in sport. For instance, as an example, we need to know our speed and velocity in running and control it so we will not get exhausted quickly. If people can control their speed, they will not have really large amount in energy.

Speed and velocity is also needed in sports such as baseball. We need to know speed and velocity in baseball to predict when the ball will arrive (speed of the ball) and the direction too. This skill is very needed for the batter so that he or she can predict the right time, the strength and the direction when hitting the ball. This is why speed and velocity is very important.

==========================================================

Written by : Celine, Darwin, Franklin and Kevin [7b].

It is important because we need skills that are connected to speed and velocity in sports. When we are playing sports like football, we need to pass the ball, run, we need power and that is connected to speed and velocity. When we want to pass the ball, we need speed and velocity so no one will keep up with you and results that no one will block your passing. When we are running, we can know the speed and velocity we are running and without speed, you will totally lose. When we need power, the faster you are, the stronger you are and the stronger you are, the more possibilities of winning. We can control the speed and velocity and that helps us in sports. In conclusion, speed and velocity is really important.

==========================================================

Written by Clarissa, William, Reyna and Belinda [7c]

In the running competition, you have to know the speed. Cyclist needs speed so that they know their speed. In a running race, you need to know that speed so that you know the winner. We need to know the velocity when we are swimming so we can defeat others. In car racing, we need to know the speed that is shown by speedometer, so we don’t drive too fast and won’t cause bad damage. We need to know the velocity of badminton ball so we can hit the ball. So, in conclusion there are so many importance of speed and velocity in Physical Education.

==========================================================
Written by Hans, Tirta, Angeline, Selma [7c]

For example in sport such as racing car. In the car they give the speedometer to read how fast the car is running. Velocity is used to know where the car is going to. Speed is importance so we know how fast is an athlete run per minute and velocity is used to know where the athlete is running. In soccer speed is used for player to run faster in the field so the player will get the ball and velocity is used to know the player direction so we can know to whom we pass the ball.

==========================================================

How to Learn Physics

For as knowledges are now delivered, there is a kind of contract
of error between the deliverer and the receiver; for he
that delivereth knowledge desireth to deliver it in such a form
as may be best believed, and not as may be best examined;
and he that receiveth knowledge desireth rather present satisfaction
than expectant inquiry.

[Francis Bacon]

Many students approach a science course with the idea that they can succeed by memorizing the formulas, so that when a problem is assigned on the homework or an exam, they will be able to plug numbers in to the formula and get a numerical result on their calculator.

Wrong! That’s not what learning science is about! There is a big difference between memorizing formulas and understanding concepts. To start with, different formulas may apply in different situations. One equation might represent a definition, which is always true. Another might be a very specific equation for the speed of an object sliding down an inclined plane, which would not be true if the object was a rock drifting down to the bottom of the ocean.

If you don’t work to understand physics on a conceptual level, you won’t know which formulas can be used when. Most students taking college science courses for the first time also have very little experience with interpreting the meaning of an equation. Consider the equation w = A/h relating the width of a rectangle to its height and area. A student who has not developed skill at interpretation might view this as yet another equation to memorize and plug in to when needed.

A slightly more savvy student might realize that it is simply the familiar formula A = wh in a different form. When asked whether a rectangle would have a greater or smaller width than another with the same area but a smaller height, the unsophisticated student might be at a loss, not having any numbers to plug in on a calculator. The more experienced student would know how to reason about an equation involving division — if h is smaller, and A stays the same, then w must be bigger. Often, students fail to recognize a sequence of equations as a derivation leading to a final result, so they think all the intermediate steps are equally important formulas that they should memorize.

When learning any subject at all, it is important to become as actively involved as possible, rather than trying to read through all the information quickly without thinking about it. It is a good idea to read and think about the questions posed at the end of each section of these notes as you encounter them, so that you know you have understood what you were reading.

Many students’ difficulties in physics boil down mainly to difficulties with math. Suppose you feel confident that you have enough mathematical preparation to succeed in this course, but you are having trouble with a few specific things. In some areas, the brief review given in this chapter may be sufficient, but in other areas it probably will not. Once you identify the areas of math in which you are having problems, get help in those areas. Don’t limp along through the whole course with a vague feeling of dread about something like scientific notation. The problem will not go away if you ignore it. The same applies to essential mathematical skills that you are learning in this course for the first time, such as vector addition.

Sometimes students tell me they keep trying to understand a certain topic in the book, and it just doesn’t make sense. The worst thing you can possibly do in that situation is to keep on staring at the same page. Every textbook explains certain things badly — even mine! — so the best thing to do in this situation is to look at a different book. Instead of college textbooks aimed at the same mathematical level as the course you’re taking, you may in some cases find that high school books or books at a lower math level give clearer explanations. The three books listed on the left are, in my opinion, the best introductory physics books available, although they would not be appropriate as the primary textbook for a college-level course for science majors.

Finally, when reviewing for an exam, don’t simply read back over the text and your lecture notes. Instead, try to use an active method of reviewing, for instance by discussing some of the discussion questions with another student, or doing homework problems you hadn’t done the first time.

What is Physics ??

Given for one instant an intelligence which could comprehend

all the forces by which nature is animated and the respective

positions of the things which compose it...nothing would be

uncertain, and the future as the past would be laid out before its eyes.
[Pierre Simon de Laplace]

Physics is the use of the scientific method to find out the basic principles governing light and matter, and to discover the implications of those laws. Part of what distinguishes the modern outlook from the ancient mind-set is the assumption that there are rules by which the universe functions, and that those laws can be at least partially understood by humans.

From the Age of Reason through the nineteenth century, many scientists began to be convinced that the laws of nature not only could be known but, as claimed by Laplace, those laws could in principle be used to predict everything about the universe’s future if complete information was available about the present state of all light and matter. In subsequent sections, Benjamin Crowell describe two general types of limitations on prediction using the laws of physics, which were only recognized in the twentieth century.

Matter can be defined as anything that is affected by gravity, i.e., that has weight or would have weight if it was near the Earth or another star or planet massive enough to produce measurable gravity. Light can be defined as anything that can travel from one place to another through empty space and can influence matter, but has no weight. For example, sunlight can influence your body by heating it or by damaging your DNA and giving you skin cancer. The physicist’s definition of light includes a variety of phenomena that are not visible to the eye, including radio waves, microwaves, x-rays, and gamma rays. These are the “colors” of light that do not happen to fall within the narrow violet-to-red range of the rainbow that we can see.

Many physical phenomena are not themselves light or matter, but are properties of light or matter or interactions between light and matter. For instance, motion is a property of all light and some matter, but it is not itself light or matter. The pressure that keeps a bicycle tire blown up is an interaction between the air and the tire. Pressure is not a form of matter in and of itself. It is as much a property of the tire as of the air. Analogously, sisterhood and employment are relationships among people but are not people themselves.

Some things that appear weightless actually do have weight, and so qualify as matter. Air has weight, and is thus a form of matter even though a cubic inch of air weighs less than a grain of sand. A helium balloon has weight, but is kept from falling by the force of the surrounding more dense air, which pushes up on it. Astronauts in orbit around the Earth have weight, and are falling along a curved arc, but they are moving so fast that the curved arc of their fall is broad enough to carry them all the way around the Earth in a circle. They perceive themselves as being weightless because their space capsule is falling along with them, and the floor therefore does not push up on their feet.

The boundary between physics and the other sciences is not always clear. For instance, chemists study atoms and molecules, which are what matter is built from, and there are some scientists who would be equally willing to call themselves physical chemists or chemical physicists. It might seem that the distinction between physics and biology would be clearer, since physics seems to deal with inanimate objects.

In fact, almost all physicists would agree that the basic laws of physics that apply to molecules in a test tube work equally well for the combination of molecules that constitutes a bacterium. (Some might believe that something more happens in the minds of humans, or even those of cats and dogs.) What differentiates physics from biology is that many of the scientific theories that describe living things, while ultimately resulting from the fundamental laws of physics, cannot be rigorously derived from physical principles.

Isolated systems and reductionism

To avoid having to study everything at once, scientists isolate the things they are trying to study. For instance, a physicist who wants to study the motion of a rotating gyroscope would probably prefer that it be isolated from vibrations and air currents. Even in biology, where field work is indispensable for understanding how living things relate to their entire environment, it is interesting to note the vital historical role played by Darwin’s study of the Galapagos Islands, which were conveniently isolated from the rest of the world. Any part of the universe that is considered apart from the rest can be called a “system.”

Physics has had some of its greatest successes by carrying this process of isolation to extremes, subdividing the universe into smaller and smaller parts. Matter can be divided into atoms, and the behavior of individual atoms can be studied. Atoms can be split apart into their constituent neutrons, protons and electrons.

Protons and neutrons appear to be made out of even smaller particles called quarks, and there have even been some claims of experimental evidence that quarks have smaller parts inside them. This method of splitting things into smaller and smaller parts and studying how those parts influence each other is called reductionism. The hope is that the seemingly complex rules governing the larger units can be better understood in terms of simpler rules governing the smaller units.

To appreciate what reductionism has done for science, it is only necessary to examine a 19th-century chemistry textbook. At that time, the existence of atoms was still doubted by some, electrons were not even suspected to exist, and almost nothing was understood of what basic rules governed the way atoms interacted with each other in chemical reactions. Students had to memorize long lists of chemicals and their reactions, and there was no way to understand any of it systematically. Today, the student only needs to remember a small set of rules about how atoms interact, for instance that atoms of one element cannot be converted into another via chemical reactions, or that atoms from the right side of the periodic table tend to form strong bonds with atoms from the left side.

Additional Learning Material for Grade 7 - 8 Students

Hi...
I'm glad to know you opening this page. I know this is your holiday, but please browse these links serves below to enrich your knowledge and raise your understanding on Physics.

By the way, I don't want to disturb your trip or holiday. But these links are very useful for you. so please check them, and read them...make Internet connection more useful for your future.

Bye ... have a nice surf...:)

Yours,
Mr Noorahmat

General Resource for Physics
Physics Classroom - The best and complete resource with common language...check it out...
HyperPhysics - for higher thinking level student
School for Champion - Easy to digest materials
Physics Based Games - this link it the best online physics game...

Grade 7
Measurement
Mass, Weight and Density
Speed and Velocity


Grade 8
Reflection of Light
Refraction of Light
Colour
Primary Colour

Physics of Sound

Magnetism
Electromagnetism

Electricity
How Electricity Work
Using Electricity
Using electricity at Home