Forces Study Guide

Average speed is fundamental to describing how fast an object is moving over a period of time, especially when that motion isn't constant. Non-uniform motion means an object's speed is changing: it might be speeding up, slowing down, or even changing direction. Unlike uniform motion where speed remains constant, calculating average speed provides a single value that represents the overall rate of travel. The key to calculating average speed is to recognise that it always relies on the *total distance travelled* divided by the *total time taken*, regardless of how the speed changed during that journey. It doesn't matter if the object stopped, started, accelerated, or decelerated; only the total distance covered and the entire duration of the journey are needed. For example, if a car travels 100 km in 2 hours, its average speed is 50 km/h. This doesn't mean it travelled at 50 km/h for the entire 2 hours; it might have gone 70 km/h for one hour and 30 km/h for another, or even stopped for a while. The formula is always: Average Speed = Total Distance / Total Time. Units must be consistent; if distance is in metres (m) and time in seconds (s), speed will be in metres per second (m/s). If distance is in kilometres (km) and time in hours (h), speed will be in kilometres per hour (km/h).

When a force is applied to an object, it can cause the object to change shape, a process known as deformation or distortion. We distinguish between two main types of deformation based on whether the object returns to its original shape once the force is removed. Elastic deformation occurs when an object returns to its original shape and size after the deforming force has been removed. Think of a rubber band: when you stretch it and let go, it snaps back. In this state, the bonds between the particles within the material are stretched but not broken, and the stored potential energy in these bonds is converted back into kinetic energy as the object recoils. The object behaves elastically up to a certain point, called the elastic limit. Beyond this limit, if the stretching force is too great, the object undergoes plastic deformation. Plastic deformation is a permanent change in an object's shape or size that remains even after the deforming force is removed. Imagine stretching a piece of soft metal wire too far; it won't return to its original length, or a clay model being squashed out of shape. In plastic deformation, the bonds between particles are permanently rearranged or broken, and internal energy is dissipated, often as heat. Understanding these differences is crucial in engineering and material science for selecting appropriate materials for specific applications, such as springs (elastic) versus structural components that must not permanently deform (requiring high elastic limit).