Forces, simply put, are pushes and pulls. They can cause things to move, speed up, slow down, change direction, or even change the shape of things. They govern everything in the universe around us. From the largest gravitational forces that hold our universe together, to the forces that keep the smallest particles in atoms together, scientists have spent millennia trying to understand forces.
There are many different types of forces that govern the world around us. They keep the atoms together that make all matter around us, they keep our planet orbiting the sun, and they stop our atmosphere from flying off into deep space.
Forces can be separated into two categories: contact and non-contact. Examples of non-contact forces are magnetism and gravity. Examples of contact forces are friction and upthrust.
The unit of force, the newton, is named after the English Scientist, Sir Isaac Newton. Newton is known as one of the most influential scientists ever. Although the story about Newton and the falling apple is likely not true, he was the first scientist to describe gravitational force mathematically. As well as his work on force and motion, Newton also made large contributions to optics, math, and biology.
Forces are vector quantities, meaning they have both a magnitude and direction. We can show forces by drawing force diagrams. With force diagrams we use arrows to show forces. The direction the arrow is pointing shows the direction the force is acting in. The length of the arrow shows the size of the force. It is also useful to label the arrow with name of the force and its size in newtons (N). Storyboard That can be easily used to produce quick and clear force diagrams for a range of different situations.
We can describe forces as being balanced or unbalanced. Balanced forces occur when forces are both equal and opposite. When forces are balanced, objects remain stationary (if they were already stationary) or continue traveling at a constant speed. When the forces are unbalanced, an object will start to move if it was stationary. If the object was already moving, then it will change speed or direction. In the first example below, the airplane would continue to travel in steady flight at a constant speed. This is because the lift has the same magnitude, but is acting in an opposite direction to the weight.
The overall force acting on an object is known as the resultant force. In the example of the airplane above, the ‘balanced forces’ example has no resultant force. In the ‘unbalanced forces’ example, the lift and weight are balanced, but the thrust is a bigger force than the drag. Thus, there will be a resultant force in the direction of the thrust.
It is useful to give a context when talking about forces. Forces on their own can be quite an abstract idea. All your students will have experienced forces in their everyday lives. Explaining forces in a familiar context, such as a car journey or a bike ride, can really help students understand. To challenge your students, give them an unfamiliar and complicated context, such as space. Ask students to look at the force at the different points of an astronaut's journey into space and home again.