#### Bonfire time

In London it's still much colder than normal for this time of year but yesterday was at least free of rain, so I decided it was time to go to the allotment and burn some things - really what can be morefun than seeing some stuff (under carefully controlled conditions and without upsetting others) burn?

Wasn't too much to set fire to apart from some woody non composting material but very satisfying and basic. The bonfire also produces potash which can be spread around to improve the soil.

#### Big Idea Newtonian Mechanics

Isaac Newton who used the phrase 'standing on the shoulders of giants' to describe his accomplishments was a notable physicist and mathematician remembered chiefly for his formulation of laws to explain motion.Newton was an interesting guy now thought to have suffered Asperger's syndrome, he lived to the age of 84 but in latter years his behaviour was eccentric, this may have been as a result of mild mercury poisoning caused by his use of the chemical in his laboratory.

The laws Newton put together related the physical concepts of force, mass, and acceleration into his three laws of motion.

1) The first law of motion holds that a body in motion tends to remain in motion, and a body at rest tends to stay at rest. This principle explains the concept of inertia, that is, the application of force that is required to move a stationary object. Similarly, the deceleration of a body, otherwise moving at a constant speed, can only occur when an outside force acts on it. For example, a projectile fired from a gun will continue its motion in a certain direction perpetually, save for the simultaneous forces of gravity and the resistance of the air in the atmosphere. These forces act together on the projectile to

make it stop at a certain distance from the spot where it was initially released.

2) Newton’s second law of motion is a mathematical or quantitative formula that describes the inherent nature of force. Newton postulated that the amount of force exerted is directly proportional to the mass of a body, times its acceleration, or

*force =mass times acceleration*. If two distinct bodies are moving at a constant acceleration, the object with the larger mass will produce the greater force. This principle of Newtonian mechanics can be illustrated by the example of a car and a train that are traveling towards each other at an equal rate of speed. When the two objects collide, the force exerted on the car will be vastly greater due to the much greater mass of the train (as in the equation).

3) Newton's third law of motion is summarised as

*for every action, there is an equal and opposite reaction*. In other words, in equilibrium the forces of two bodies acting upon each other are always equal and directly opposite. For instance, the force that a baseball exerts on a bat is equal and opposite to the force that the bat exerts on the baseball.

Although Newton's 'laws' hold good for most cases some say that they do not work at sub-atomic particle level or where the bodies are at velocities around the speed of light.