## A formula of force

Posted June 29, 2009

on:- In: Physics | Science
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There is one totally important formula when it comes to forces,

**F = ma**

That’s all there is, but everything revolves around that formula. “F” is the total (net) **force**, “m” is the object’s **mass**, and “a” is the **acceleration** that occurs. As a sentence, “The net force applied to the object equals the mass of the object multiplied by the amount of its acceleration.” The net force acting on the soccer ball is equal to the mass of the soccer ball multiplied by its change in velocity each second (its acceleration). Do you remember the wind gently blowing on the soccer ball? The force acting on the ball was very small because the mass of air was very small. Small masses generally exert small forces, which generally result in small accelerations (changes in motion).

Further info here:

http://www.physics4kids.com/files/motion_force.html

## blood

Posted June 19, 2009

on:- In: Biology | Science
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Red cells (erythrocytes). These make blood a red colour. One drop of blood contains about five million red cells. Red cells contain a chemical called haemoglobin. This binds to oxygen, and takes oxygen from the lungs to all parts of the body.

## Simultaneous equations

Posted June 10, 2009

on:A simple example:

3x + y = 10 equation 1

2x + y = 7 equation 2

STEP 1 – We subtract equation 2 from equation 1 (so we eliminate the y’s)

a) 3x -2x = x, b) y-y=0, c) 10-7 = 3 and we are left with:

x = 3

STEP 2 – we SUBSTITUE the value of x (which is 3) into equation 2 as follows:

2x + y = 7

2*3 + y = 7

6 + y = 7

(-6) y = 7-6

y = 1

## The Hydrogen Atom

Posted June 5, 2009

on:- In: Physics | Science
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## Momentum

Posted June 5, 2009

on:- In: Science
**2**Comments

**Momentum**

Momentum = mass x velocity

the equation is:

P = mv

Remember the units of mass and velocity:

Units of mass: Kg

Units of velocity: m/s

Thus the units of momentum are:

Kg m / s

Newtons cradle is a good example of the principle of “conservation of momentum”:

## Mass and weight

Posted June 5, 2009

on:## Weight and Mass

What’s the difference between weight and mass?

As long as you stay on Earth, the difference is more philosophical than practical.

Uh…what do you mean by that?

Well, mass is a measurement of how much matter is in an object; weight is a measurement of how hard gravity is pulling on that object. Your mass is the same wherever you are–on Earth, on the moon, floating in space–because the amount of *stuff* you’re made of doesn’t change. But your weight depends on how much gravity is acting on you at the moment; you’d weigh less on the moon than on Earth, and in interstellar space you’d weigh almost nothing at all.

But if you stay on Earth, gravity is always the same, so it really doesn’t matter whether you talk about weight or mass.

That’s right…but scientists still like to be careful about distinguishing between the two. If you talk about the mass of an atom–as I will do from now on–you’re always talking about the same thing; if you talk about its weight, what you mean depends on where the atom is.

Here is a graphical example. The * mass* stays the same, but

*can change.*

**weight**