1.13. Summary

Force Push or pull; S.I. unit – Newton

Force is defined as a push or pull that can cause an object to change its state of motion. The standard unit used to measure force is the Newton (N). This means that whenever we talk about the effect of force, we can quantify it using this unit. Whether an object is moving, stationary, or changing direction, it is the application of force that brings about these changes.

Imagine using a shopping cart. When you push the cart, you are applying force, which moves it forward. If you pull it back, that is also a force acting in the opposite direction. Without force, the cart would remain still.

Moment Turning effect; Moment = Force × Distance

The moment of force, or simply 'moment', refers to the turning effect that a force generates about some pivot point. Mathematically, it is calculated as the product of the force applied and the distance from the pivot point to the line of action of the force. This means that both how strong the force is and how far away the force is applied from the pivot point matter when determining how effectively a force can cause rotation.

Think of a door. When you push on the doorknob (which is farther from the hinges, the pivot point), it opens more easily than if you push near the hinges. This shows how the distance affects the moment.

Equilibrium Resultant force = 0; Principle of Moments holds

An object is said to be in equilibrium when the net or resultant force acting on it is zero. This means that all the forces are balanced and there’s no unbalanced force acting on the object, which leads to no change in its state of motion. The principle of moments also applies here: for an object to be in equilibrium, the sum of clockwise moments around a point must be equal to the sum of anticlockwise moments.

Imagine a seesaw. It will balance evenly when equal weights are placed at equal distances from the pivot point. If one side has more weight or is farther away, it will not be in equilibrium and will tilt.

Centre of Gravity Point where weight acts; affects stability

The centre of gravity (C.G.) is the point in an object where its weight is effectively concentrated. It plays a crucial role in determining how stable an object is. For example, a lower centre of gravity generally leads to greater stability, while a higher C.G. can lead to an increased risk of tipping over. Factors such as the base area and height of the C.G. influence the stability of an object.

Consider a tall, narrow tower versus a short, wide building. The short building has a lower centre of gravity and is less likely to topple over in strong winds compared to the tall tower.

Levers & Pulleys Simple machines; M.A., V.R., and efficiency explained

Levers and pulleys are types of simple machines that help us lift or move loads with less effort. The Mechanical Advantage (M.A.) of a machine is the ratio of the load it lifts to the effort applied. The Velocity Ratio (V.R.) is the ratio of the distance moved by effort to the distance moved by load. Understanding these concepts helps us evaluate how efficiently a machine works.

Think of using a lever, like a seesaw. If you place a heavy load on one side and apply a small effort on the other, the lever allows you to lift that heavy load fairly easily. In this case, the lever increases your efficiency by allowing you to use less force.

In daily life – scissors, wheelbarrows, cranes, etc.

The concepts of force, moments, equilibrium, centres of gravity, levers, and pulleys are not just theoretical; they apply directly to everyday tools and devices. Scissors are levers that cut, wheelbarrows are pulleys that reduce effort, and cranes exemplify how force and stability can be managed to lift heavy objects safely. These principles help us understand how various machines work, making our tasks easier.

When you use a wheelbarrow to carry heavy dirt in your garden, you can notice how the design helps you lift more with less effort. The wheel acts like a pulley, helping to distribute the load and reduce the force you need to exert.

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