Motion and Time: Formulas, Units & Sample Questions

Motion and Time are two different terminologies in Physics that are usually correlated with one another in many aspects. In our everyday lives, we see many things moving or in motion, for example, automobiles on the road, birds flying, animals walking, fish swimming etc. All these activities of these things are perceived as motion since these objects are changing their position with respect to time.

Key Terms: Motion, Time, Speed, Acceleration, Uniform Motion, Non-Uniform Motion, Periodic Motion, Time Period 

What is Motion?

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Motion can be defined as the change in the position of an object with respect to time. On the other hand, if an object is not perceived to be changing its position with respect to time, then it is said to be at rest. 

Motion

Some of the important terms related to motion are described below:

• Distance: Distance can be defined as the total path covered by an object in a particular interval of time. For example, if a car starts moving from around A point and stops at point B, then the total distance covered by the car is equal to the distance between the two points A and B. Mathematically, Distance = Speed x Time
• Displacement: Displacement can be defined as the shortest route or path covered by an object in a given time interval. Also, if the starting and end points of the route taken are the same, then the displacement is said to be zero.
• The standard unit of distance is in metres whereas the standard unit of time is in seconds.

Distance and Displacement 

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Types of Motion

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Mentioned below are the types of motion:

• Rectilinear/Translatory Motion: Translatory/ Rectilinear motion can be defined as the motion of an object in a straight line without a change in direction. For example, if a car is moving along a straight road without any change in its direction, then the movement of that car is said to be rectilinear or translatory.
• Circular Motion: Circular motion can be defined as the motion or movement of an object along a fixed circular path with a fixed radius. In this case, if the moving object comes back to its initial position, then its displacement is said to be zero. For example, the movement of wheels of an automobile, planetary motion etc.
• Rotational Motion: This type of motion can be defined as the movement of an object around a fixed axis. For example, spinning top, blades of a moving fan etc.
• Periodic or Oscillatory Motion: Periodic or Oscillatory motion can be defined as the motion in which the moving object repeats its movement after a fixed interval of time. For example, the to and fro movement of the bob of a pendulum, the motion of planets around the sun etc.

Types of Motion

Read More: Simple Harmonic Motion

Oscillations of a Simple Pendulum

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We all know that the bob of the simple pendulum follows oscillatory or periodic motion since it repeats its movement after a fixed time interval. 

• The bob of the pendulum is said to complete one oscillation when it moves from its mean position B to A and back to B again, then from B to C and back to B again.
• The time period of a simple pendulum in this case can be defined as the total time taken by the pendulum to complete one oscillation.

Oscillations of a Pendulum

Uniform and Non-Uniform Motion

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The definitions for uniform and non-uniform motion are as follows: 

• Uniform Motion: An object moving along a straight line with a constant speed is said to be in uniform motion. For example, the motion of a car with a constant speed in a straight line.
• Non-Uniform Motion: An object moving along a straight line with a variable speed is said to be in non-uniform motion. For instance, the motion of a train/bus.

Read More: Motion in a Straight Line

Speed and Time

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• Speed

The speed of an object can be defined as the distance travelled by the object per unit of time. An object in motion can have a variable speed depending upon the distance covered by it in a particular interval of time. The standard unit of speed is metres per second. Mathematically,

Speed = Distance Covered by the Object / Time Taken to Cover the Distance

For example, if a moving car covers a distance of 100 km in 2 hours, then its speed can be calculated by using the above formula, which is equal to 50km/h. 

• Time

Time in physics can be defined as the duration over which change occurs. The time taken by the object to cover a particular distance also depends upon its speed. The standard unit of time is seconds. Mathematically,

Time = Distance Covered by the Object / Speed of the Object

For example, if a car is moving with a speed of 50 km and covers a distance of 100 km, then the time taken by the object can be calculated by using the above formula, which is equal to 2 hours.

Speed, Distance and Time Formulas

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Things to Remember

• An object is said to be in motion if the position of the object changes with reference to time.
• The motion of a freely falling body is said to be linear motion.
• The time period of a simple pendulum also depends upon its length and acceleration due to gravity.
• Slow and fast objects can be differentiated from each other by looking at the time taken by each object to cover a particular distance.
• The distance-time graph for a non-uniform motion is a curved line.
• The distance-time graph for a uniform motion is presented as a straight line.
• Speedometer is a speed measuring device that is usually seen on the dashboard of automobiles. It measures the speed of automobiles in motion.
• Odometer is an instrument used for measuring the distance travelled by the object.