forces

whenever planes hurtle overhead or cars screech to a halt, forces are working hard behind the scenes. on a larger scale,gravitational force  span the universe,causing stars to cluster into galaxies and keeping planets whirling in orbit around the sun. at the other end of the scale,atoms cause forces like sticking and friction.

what is force 

a force is a push or pull that make something happen. when you kick a ball,your foot supplies the force the makes the ball fly into the air. forces are usually invisible. gravity is the invisible that pins us to ground ,while magnetism is another hidden force that makes a compass spin. simple forces can change an objects shape ,after  its direction,or change its speed.