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# Newton’s First Law of Motion – Law of Inertia

While Newton’s principles of motion may appear simple to us now, they were revolutionary centuries ago. The laws of motion explain how things behave when they are stationary, moving, or under the influence of forces. The Laws of Motion of Newton are described in this page, along with a synopsis of what they signify.

The laws of motion define the connection between a body and the forces that operate on it, as well as motion of the body in response to those forces. To be more explicit, the first rule of motion describes the force qualitatively, the second law of motion quantifies the force, and the third rule of motion asserts that there is no such thing as a single isolated force.

### Newton’s First Law of Motion

Newton’s first law says that a body at rest or in uniform motion will remain at rest or in uniform motion until and unless it is subjected to a net external force.

Galileo’s law of inertia is another name for Newton’s First Law of Motion. Unless driven to change its condition by an external force, a body remains in its condition of rest or uniform motion along a straight line. The force is defined in the law as a factor that can modify the condition of an item.

Inertia is a quality of a body that prevents it from changing its state. The inertia of translational motion is measured by a body’s mass.

A body of more mass has a harder time changing its condition of rest or uniform motion, and vice versa.

• The mass of a body is a numerical or quantitative measure of its inertia.
• The greater a body’s inertia, the greater it’s mass.

Newton’s first law of motion

The First Law of motion depends on three conditions:

1. Inertia of Rest: An object at rest tends to remain at rest unless an external force acts on it.

Examples:

• The rider falls backward when a horse starts suddenly.
• Mangoes fall from mango tree branches when we shake them.
• When a blanket is thrashed with a stick, the dust particles fall off.
• Passengers on board a bus or train tend to fall back when the vehicle begins rapidly.
• A coin is placed on cardboard, which is then placed over a tumbler such that the coin is above the tumbler’s mouth. The coin now falls into the tumbler if the cardboard is removed with a sharp movement.

2. Inertia of Motion: An object in motion tends to remain in motion unless an external force acts on it.

Examples:

• A bowler runs the ball before throwing it, so the speed of the run is added to the ball’s speed at the moment of the throw.
• Passengers on a bus or train lean forward when it comes to an abrupt halt.
• An athlete runs a specific distance before attempting a long jump because the velocity gained while running is added to the athlete’s velocity at the moment of the leap, allowing him to jump further.
• A ball tossed upward by a passenger onboard a moving train will fall according to the train’s speed.
• When a person leaps off a moving train, he or she may fall forward.

3. Inertia of Direction: A body can’t change its motion direction on its own.

Examples:

• The sparks created when a knife is rubbed against a grinding stone move in a tangential direction.
• Mud is spat out by the vehicle’s rotating wheels, but mudguards installed over the wheels prevent the mud from spreading.
• When a straight-running automobile makes a quick turn, the occupant feels a force radiating outwards.

### What is an External Force?

A force is defined as the push or pulls that affects or tends to modify the condition of rest or uniform motion (constant velocity) of a body, according to Newton’s first law of motion.

An external force is one that originates from outside an item rather than one that originates from within it. The force of gravity exerted by Earth on the moon, for example, is an external force on the moon.

The force of gravity exerted by the moon’s inner core on its outer crust, on the other hand, is an internal force on the moon. Internal forces within an object cannot alter the overall motion of the item.

Effects of Resultant force:

• It has the potential to alter the direction of motion.
• It has the potential to alter the body’s speed.
• It has the ability to modify the direction as well as the speed of motion.
• It has the ability to start or halt motion in a stationary body.
• It has the potential to alter the size and/or form of the body.

### Newton’s First Law of Motion Examples in Daily Life

Some daily life examples are as below:

• Assume we’re aboard a bus that isn’t moving. We will sense a jolt in the rearward direction if it starts moving suddenly. Because our body is in touch with the bus seat and moves with the bus’s motion, but the upper half of our body remains at rest owing to inertia, we experience a jolt in the rearward direction.
• A book on a table cannot shift its position until a force is applied to it.
• If we push a ball on the ground, it should continue moving consistently eternally, but it stops after a certain distance has been covered. As soon as the ball begins to move, a force (friction force) is created that resists the ball’s motion.
• On a card, a tiny coin is placed over a glass. The penny falls into the glass when the card is flicked aside with the finger.

### Sample Problems

Problem 1: Why do Objects Slow Down?

Solution:

The slowing down of items was thought to be an inherent characteristic of the things prior to Newton and Galileo. Friction and gravity were unknown forces at the time. The frictional force resists an object’s motion, causing it to lose energy and hence slow down.

When we watch a toy car traveling on a concrete surface, for example, the speed of the automobile is governed by the friction between the road and the vehicle wheels. The wheel will meet with little resistance when the toy automobile is driven over a smooth surface. This will create a frictional hurdle, allowing the automobile to accelerate across the entire plain tile surface.

This is in stark contrast to when a vehicle toy is driving on a slick, gravel-filled terrain. The idea of change in the condition of rest or motion is defined by Newton’s first law of motion.

Problem 2: What is Newton’s first law of motion?

Solution:

Newton’s first law of motion states that a body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force.

Problem 3: What is motion?

Solution:

The change in position of a body/object with regard to time is known as motion. Distance, displacement, speed, velocity, and acceleration are the characteristics used to characterize motion.

Problem 4: What do you mean by force?

Solution:

A force is defined as the push or pull that affects or tends to modify the condition of rest or uniform motion (constant velocity) of a body, according to Newton’s first law of motion.

Problem 5: What is inertia?

Solution:

A characteristic of matter that allows it to remain in its current condition of rest or uniform motion in a straight line until it is disrupted by an external force is called an inertia.

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