Forces and motion

FORCES Push, pull , press and move things.Forces have size or strength – and also direction.A force always acts on an object in a particular direction.If the object is free to move, the force makes it move and speed up, or accelerate,in the direction of the force.When something cannot move,such as a nut in the jaws of a nutcracker the forces can change its shape or even break it altogether.

kick a soccer ball, and you force it to move. Once going, the ball tries to carry on in the same direction at the same speed. But two froces on it, to change both speed and driection. The are air resistance and gravivty. Kicking a ball shows three of the most basic ideas in all of science — the laws motion.The first law of motion says that an object continues to move in the same direction, at the same speed, unless forces act on it.Kick a ball, and the forces of gravity and air resistance (as the ball pushes its Way through molecules of air) make it slow and fall down, The second law of motion says that the greater the force on an object picks up speed.That is acceleration of an object is proportional to the force acting on it.So kick harder, and the ball goes faster. The third law of motion says that when an object hits another the second object produces an equal force but in the opposite direction. In other words, for every action, there is an equal and opposite reaction. If two soccer balls hit each other rolling at equal speeds in exactly opposite directions they bounce apart and roll back the way they came. As two teams battle in a tug-of-war, they pull with their arms, but they also lie back as far as they can. This increases the force of their pull, by adding their weight to the power of their leg muscles pushing against the ground. Some buildings are fixed into the ground by steel girders called piles. driven in by a machine case a pile driver. The weight of the pile ‘s like a giant hammer, hitting to go and again with tremendous force,pushing it deeper into the earth Dropping the pile weight from a greatre height increases the force of e blow, which is why pile-drivers * all towers. As the pile goes in,the weight has farther to fall. A car-crusher produces such enormous forces that it presses a whole vehicle into a small cube. This saves space at refuse dumps. But a better answer is more recycling. Tracks in soft ground show where an animal walked.The pressure of the animal’s weight acting through its feet overcame the ability of the ground to resist it,and the animal sank in slightly. The same animal with smaller feet would make deeper tracks, because the same weight acts over a smaller area, producing greater pressure. Heavy vehicles on soft ground often have wide “caterpillar tracks.These spread the vehicle’s weight over a large area, compared to wheels with tyres, so the vehicles sinks is less.Working animals like oxen and buffalo have wide hooves, for the same reason.