# Effects of Forces

### Forces and resultants

The resultant force is the single force that has the same effect as 2 or more forces.

To make the picture simpler, let’s take a look at the example below:

There is a box which needs to be pushed across a room.

You apply a force of 10N to push a car. As it is pushed, there is a force of 5N caused due to friction acting on the car as well. Hence here the resultant force will be 10N-5N = 5N to the right.

### Newton's first law: Mass and Inertia

According to Newton's First Law of Motion, unless acted upon by an outside force, an object will remain at rest or continue to travel in a straight path at a constant speed. The concept of inertia is another name for it.

An object's inertia is the ability to resist changes in its state of motion. Unless a force is given to a stationary item, it will stay that way. Until an outside force is used to alter an object's state of motion, it will continue to move at a constant velocity (which includes speed and direction).

Let's take a look at this through an analogy:

Imagine playing with a toy car on an even, smooth surface. You know how the automobile starts to roll when you give it a little push? And it moves quicker if you exert a little more force. What occurs, though, if you stop pushing it? Right, finally the automobile slows down and comes to a stop.

Imagine playing the same game, except this time the road is extremely slippery with ice. When you give it a little push, it quickly begins to slide. What happens if you abruptly stop pushing the car? Well, it continues to slide for a while before stopping, doesn't it?

The cool part is that Newton's First Law is similar to saying that if you were to play this game on a surface with zero friction (no roughness or stickiness), as soon as you push the vehicle, it would just keep sliding forever without slowing down! A push from anything like your hand would cause the automobile to move if it were simply sitting there.

### Newton's second law: Effects of force and mass on acceleration

The connection between force, mass, and acceleration is described by Newton's second law of motion. It asserts that an object's acceleration is inversely proportional to its mass and directly proportional to the net force applied on it. This law may be written mathematically as:

```
F = ma
```

Where:

**F** -> force (measured in N, Newton)

**m** -> mass (measured in Kg, Kilogram)

**a** -> acceleration (measured in m/s^{2}, meters per second squared)

Worked example:

When you strike a tennis ball that another player has hit towards you, you provide a large force to reverse its direction of travel and send it back towards your opponent. You give the ball a large acceleration. What force is needed to give a ball of mass 0.1 kg an acceleration of 500m/s^{2}

Step 1: We have:

```
mass = 0.1kg
acceleration = 500 m/s^2
force = ?
```

Step 2: Substituting in the equation to find the force gives

```
force = mass x acceleration
= 0.1 kg x 500 m/s^2
= 50 N
```

__Force and Acceleration__: Assuming an object's mass stays constant, it will accelerate more if you apply more force on it. This implies that an object's acceleration is directly proportional to the force acting on it. For instance, a car will accelerate more quickly if you push it with more effort.

__Mass and Acceleration:__ If the force acting on an item does not change, an object's acceleration will increase as its mass increases and decrease as its mass decreases. In other words, mass has an inverse relationship with acceleration. For instance, when pushed with the same force as a heavier item, the lighter object will accelerate more quickly.

### Extension in Springs

Hooke's Law describes the behaviour of springs when they are stretched or compressed. Think of a spring as being similar to those found in a mattress or pen. A spring is in its normal state when it is just sitting there. However, you would expect it to grow or shrink if you pulled or pushed on it.

Hooke's Law explains how much a spring will stretch or compress when a force is applied to it. According to this, the force we provide is directly proportional to the force we apply. This means that the spring will stretch or compress twice as much if you pull or push twice as hard.

*When* a force is given to an elastic solid, as a straight metal wire, proportionality holds as long as the solid is not irreversibly stretched. The load-extension graph becomes nonlinear at the limit of proportionality because the extension is no longer proportionate to the stretching force.

### Circular Motion

Consider yourself on a merry-go-round. You have a sense of being pushed outward, away from the centre, when the merry-go-round begins to spin. You could be left wondering why you don't get thrown off!

Well, **centripetal force** enters the picture here. Because of inertia, which is the propensity for things to continue doing what they are already doing, your body wants to keep going straight forward while the merry-go-round revolves. In this scenario, you would continue to move away from the merry-go-round's centre in a straight path.

Centripetal force is therefore like a helpful friend on the merry-go-round, keeping you safely spinning without being thrown aside. It is the force that keeps things moving in circles and prevents them from taking off in a straight line.

### Friction

Friction is like a helpful stop sign or a speed bump. Things may be slowed down or stopped by it, and it can even help you keep your balance. So know that whenever you're holding a pencil, pulling a cart, or bicycling uphill, friction is at play.

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