Forces are pushes and pulls For example, when you do homework, you exert a force on your pen or pencil, because you push and pull it across the paper.
A force results from the interaction between two objects. A force can be defined as a push or a pull which acts upon an object as a result of its interaction with another object.
When one object exerts a force on another object it always experiences an equal opposing force in return from the object it exerted the force on. Or in other words when two objects interact, the forces they exert on one another are equal and opposite. These forces are referred to as the action and reaction forces.
Forces are measured in units called newtons (N). The unit is named after the famous physicists Sir Isaac Newton (1642-1727) who Laws of Motion are instrumental in understanding the effects of forces.
Weight
Weight is the force of gravity, which is the pull of the Earth on an object. To understand the force of gravity the concept of mass needs to be understood as well.
The mass of an object is the amount of matter it contains. Thus mass is a measure of how much stuff is in an object. Mass is measured in kilograms (kg) and is the same no matter where the object is located in the universe. For example and object of mass 10kg on the Earth will have the same mass of 10kg on the moon or anywhere else in the universe. Weight on the other hand is a measure of the pull of a planet i.e. Earth on the stuff contained in the object. The direction of the force of gravity is downwards towards the centre of the Earth.
As mentioned earlier when two objects interact they exert equal and opposite forces. The force that opposes the force of gravity in called the Reaction Force. This is equal to the force of gravity and acts in an upwards direction (opposite to the downwards direction of the force of gravity). This is exerted by the object on the earth.