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When an object changes its position relative to a fixed point, it is said to be in motion. The motion of the object can be slow or fast depending on factors such as its speed, position, direction and acceleration. Motion is a relative concept and thus, whether the object has a slow motion or fast motion also depends on the position of the observer.
Also Read: Speed, Distance and Time Formula
| Table of Content |
Key Terms: Motion, Speed, Acceleration, Velocity, Direction, Distance, Time, Periodic Motion
Slow and Fast Motion
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Slow motion refers to the movement of an object which takes a long time to cover a certain distance. While another object which takes a shorter time to cover the same distance is known to have a fast motion.
For Example: To cover a distance of 30 km on a bicycle will take around 20-30 mins while it will only take around 10 mins from a bus. Thus, a bus moves faster than a bicycle.
Examples of Slow and Fast Motion
To find out which of the two objects is moving faster, quantities like their speed and distance travelled by them in a unit amount of time are necessary.
Also Read: Frames of Reference
Types of Motion
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Not every object exhibits the same type of motion. There are four different types of motions that an object can exhibit, and they are discussed below.
- Rectilinear Motion: If an object moves in a straight line, it is said to be in a rectilinear motion.
Rectilinear motion
- Circular motion: When a body moves along a circular path, the motion it possesses is called circular motion.
Circular motion
- Rotational motion: When a body spins about a fixed axis, it is known to be in rotational motion.
Rotational motion
- Periodic motion: The motion which is repeated after regular intervals of time, is called periodic motion.
Periodic motion
Also Read: Measurement of Time
Examples of Motion
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Examples of motion can be found around us all the time. A few examples are given below.
- A ball rolling down the road.
- An aeroplane flying in the sky.
- People walking or jogging.
- A ship sailing in an ocean.
- A car moving on the road.
Also Read:
| Related Topics | ||
|---|---|---|
| Scalars and Vectors | Equation of Motion | Relative Speed |
| Drift Velocity | Acceleration and Velocity | Displacement Formula |
Speed, Velocity and Acceleration
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The motion of an object is determined by its speed, the distance travelled, the time taken and many other things. Of all the factors, speed is the most convenient way to determine whether an object is moving slowly or fastly.
Speed
The rate at which an object changes its position or covers a certain distance, is known to be its speed.
- Speed is the quantity that determines how slow or fast the motion of the moving object is.
- An object in fast motion would have a high speed and will cover a longer distance compared to an object moving slowly with a low speed, in the same period of time.
- An object that isn’t moving at all has zero speed.
The first person to give a formula for speed in terms of the distance covered in a period of time was Galileo.
The formula for speed is:
Speed = Distance/Time
Speed is a scalar quantity which means it has magnitude but no direction. The S.I. unit of speed is Kilometers per hour or Km/h. But it can be expressed in many other units as well. Some of these units are:
- Miles per hour or mi/h
- Metres per second or m/s
- Light years per century
The fastest animal on land with the highest speed is Cheetah. The maximum speed at which it can travel is close to 100 km/hour. Speed is always a positive number and can not be negative.
Also Read: Speed Time Graphs
Velocity
Velocity is also defined as the rate at which a body changes its position just like the speed but it is a vector quantity. Thus, velocity has both the magnitude as well as the direction, unlike speed which only has the magnitude.
For Example, if a person is taking one step forward and one step back his velocity is zero, since the motion results in zero position change. Thus, when mentioning the velocity of any object, the direction of its motion should be stated as well. If we say that the bus is moving at 60 km/hr, it does not completely express its velocity. But 60 Km/hr West is a velocity.
Also Read: Instantaneous Velocity Formula
Acceleration
The acceleration of an object is defined as the change in its velocity per unit of time. The formula for acceleration is given as:
Acceleration = change in velocity/time.
Acceleration appears at both times, during increment as well as decrement of speed. When speed is reduced by applying brakes on a vehicle, the reduced acceleration is termed deceleration. It is also a vector quantity, and a change in direction also results in acceleration.
The unit of acceleration meters per second square or m/s2.
Also Read: Centripetal Acceleration
Things to Remember
- Motion of an object is its change in position relative to a fixed point.
- Motion is a relative concept and solely depends on the point of observation.
- Periodic motion is defined as the motion which is repeated after regular intervals of time.
- Generally, objects with high-speed exhibit fast motion and objects with relatively low speed, exhibit slow motion.
- Velocity is a vector quantity and thus the direction of motion must be stated while mentioning an object’s velocity.
Sample Questions
Ques: What is momentum? [2 marks]
Ans: Momentum is defined as the product of the mass of the moving object and its velocity. It is a vector quantity, having both a direction and a magnitude.
Ques: Define instantaneous speed. [2 marks]
Ans The speed of a moving object at a given instant of time is called its instantaneous speed. For uniform motion, instantaneous speed is constant. It is also a scalar quantity and has m/s as the S.I. unit.
Ques: What is a uniform motion? [3 marks]
Ans: Uniform circular motion of an object is defined as its motion when it moves around in a circular path at a constant speed. It covers the same linear distance every instant of time. The object traverses distance around the perimeter of the circular path. So, if a bus is said to have a speed of 6 meters/second in a circular motion, the bus is moving 6 meters every second around the perimeter of the path. The distance covered by the object in one complete cycle around the path is equal to the circumference of the circle.
Ques: What is speed? If a bicycle is moving at a speed of 10 km/h, at what time will it complete a 45 km long journey? [3 marks]
Ans: Speed is defined as the rate of distance travelled. It is a scalar quantity and has the S.I unit of m/s.
Speed of the bicycle = 10 km/h and distance it needs to travel = 45 km
Therefore, we know that: speed = distance travelled/time
Thus, time taken = 45/10 = 4.5 h
Thus the bicycle will take 4.5 hours to reach its destination.
Ques: What type of motion is of a fan? [2 marks]
Ans: A fan rotates on its axis and thus it exhibits a rotational motion but the fan blades have a circular motion as they move in a circle with a fixed radius attached to the centre.
Ques: How are velocity and speed different from each other? [2 marks]
Ans: Speed is defined as the rate of change in distance and is a scalar quantity. While velocity is the rate of change in the position of an object and is a vector quantity. Speed only has th magnitude whereas velocity has both magnitude and direction. Speed is always positive and can never be zero, but velocity is both positive and negative.
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