Linear motion

Things can move in a straight line.

This is called linear motion. An athlete can run this way on a track. They move in one direction and do not turn.

Some things move at the same speed. Other things change speed. This change is called acceleration.

Forces can change how things move. Gravity can pull on an object. Friction can also slow things down.

We use metres to measure how far things go. It is a simple way to study movement. It helps us understand our world.

Linear motion is movement along a straight line. It is the most basic type of motion. An athlete running a 100-meter dash is a good example.

There are two ways to move in a line. You can have uniform motion. This means you move at a steady velocity. Velocity is how fast you move in one direction. You can also have non-uniform motion. This happens when your velocity changes. This change is called acceleration.

We use displacement to measure how far you go. Displacement is the shortest path from start to finish. We measure this in metres. If you walk to work and come back home, your displacement is zero. This is because you ended where you started.

Scientists also study how acceleration changes. If acceleration changes, it is called jerk. In the UK, people call this jolt. If jerk changes, it is called jounce.

Newton's first law helps us understand this. It says objects keep moving in a straight line. They only change if a force acts on them. Gravity and friction are common forces. They can change how an object moves.

Linear motion is the most basic way things move. It is also called rectilinear motion. This happens when an object moves along a straight line. You can describe this motion using only one dimension. A great example is an athlete running a 100-meter dash on a straight track. This type of movement is very important in science. It helps us understand how everything else in the world moves.

There are two main ways this motion works. First is uniform linear motion. This means the object has a constant velocity. In this case, there is zero acceleration. Second is non-uniform linear motion. This happens when the velocity changes. This change is called acceleration. Newton's first law of motion explains this well. It says objects keep moving in a straight line if no force acts on them. Forces like gravity or friction can change this motion. These forces can make an object stop or turn.

Scientists use special words to measure this movement. Displacement is the shortest path from a start point to an end point. We measure displacement in metres. If you walk to work and return home, your displacement is zero. This is because you ended where you started. Velocity is how fast you move in one direction. The magnitude of velocity is called speed. We measure speed in metres per second. You can find average velocity by dividing total displacement by total time.

We can also look at how motion changes very quickly. Acceleration is the rate at which velocity changes over time. Its unit is metres per second squared. If acceleration changes, it is called jerk. In the UK, people call this jolt. If jerk changes, it is called jounce. Scientists can use math to link these ideas. For example, they use equations of motion for constant acceleration. These equations connect acceleration, velocity, time, and displacement.

Linear motion is different from other types of movement. In general motion, objects move in many directions. In linear motion, all directions stay the same along one axis. You can also compare it to rotational motion. Rotational motion happens when something turns around a fixed axis. While linear motion uses distance, rotation uses angular displacement. Scientists use math to show how these two types of motion are similar. This helps us understand both straight lines and spinning objects.

Linear motion, also known as rectilinear motion, is the most fundamental way an object moves. It occurs when an object travels along a single straight line. Because the path is straight, scientists can describe this movement using only one spatial dimension. This makes it much simpler to analyze than general motion. In general motion, an object's position and velocity are vectors with both magnitude and direction. In linear motion, all direction components remain equal and constant along a single axis. This means we can focus only on the magnitude of the movement.

There are two primary categories of linear motion based on velocity. The first is uniform linear motion, where the object maintains a constant velocity. In this state, the object experiences zero acceleration. The second type is non-uniform linear motion, where the velocity changes over time. This change in velocity is known as acceleration. According to Newton's first law of motion, an object will continue in a straight line at a constant velocity unless a net force acts upon it. In our daily lives, external forces like friction or gravity often act on objects. These forces can change an object's direction or speed, moving it away from simple linear motion.

To study this motion, we use several specific measurements. Displacement is the change in position from a starting point to an ending point. It is the shortest distance between these two points. We measure displacement using the SI unit of the metre. It is important to distinguish displacement from total distance traveled. For example, if a person travels to work and then returns home, their total distance is not zero. However, their overall displacement is zero because they ended exactly where they started.

Velocity describes the rate at which displacement changes over a specific interval of time. Velocity is a vector quantity, meaning it includes both a magnitude and a direction. The magnitude of velocity is simply called speed, measured in metres per second. We can calculate average velocity by dividing the total displacement by the total time taken. If we want to know the velocity at one exact moment, we calculate instantaneous velocity. This is found by letting the time interval approach zero. The magnitude of this instantaneous velocity is the instantaneous speed.

Acceleration is the rate at which velocity changes with respect to time. It is measured in metres per second squared. Mathematically, acceleration is the second derivative of displacement. If the acceleration itself changes, we call that rate of change "jerk." In the United Kingdom, jerk is sometimes called "jolt." If the rate of jerk changes, it is known as "jounce," measured in metres per quartic second. These terms describe how smoothly or abruptly a change in motion occurs.

When acceleration is constant, we can use specific equations of motion. These equations link acceleration, velocity, time, and displacement together. We can also visualize these relationships using graphs. On a displacement-time graph, the gradient of the line represents the velocity. On a velocity-time graph, the gradient represents the acceleration. Furthermore, the area under a velocity-time graph tells us the total displacement. The area under an acceleration-time graph represents the change in velocity.

Linear motion is often compared to rotational motion to understand complex systems. While linear motion happens along a line, rotational motion happens around a fixed axis. There are many mathematical analogies between the two. For instance, linear displacement is equivalent to angular displacement, which is measured in radians. Linear velocity corresponds to angular velocity, and linear acceleration relates to angular acceleration. Even concepts like mass in linear motion have an equivalent in rotation called the moment of inertia. Understanding these connections allows scientists to apply the same logic to both straight and spinning movements.