A force can be defined as a push or a pull. It is an action which causes a change in shape, size or motion of an object or system. Force is measured in Newtons (N).
Types of forces
Forces are divided into two groups:
- Contact forces - these require the objects involved in the interaction to be in physical contact with each other. Examples include:
- friction
- tension
- air resistance
- Non-contact forces - these can be applied at a distance, requiring no contact between the object exerting the force and the object experiencing the force. Examples include:
- gravitational force (between any two bodies with mass)
- magnetic force (between magnetic materials)
- electric force (between charged bodies)
Weight
Weight is the force exerted by the Earth (or another planetary body) on the objects within its gravitational field. It can also be thought of as the force exerted by a body on another body which is supporting it – assuming that the bodies are within a gravitational field. Weight can be calculated as the product of the object’s mass and the Earth’s gravitational acceleration ($g$): $$ \begin{equation}\begin{aligned} Weight=&mass\times acceleration\ due\\\ &to\ gravity\\ W=&mg\\ \end{aligned}\end{equation} $$
Recall that $g$ is approximately $9.81\ ms^{-2}$.
Mission details
Determine the weights of the following objects:
- $3\ kg$ bag of rice
- $0.4\ kg$ ball
- $50\ g$ coin
Remember to use to the SI units for each physical quantity involved