These DAV Class 7 Science Notes and DAV Class 7 Science Chapter 6 Notes – Motion and Time act as excellent revision resources, particularly in preparation for board exams.
Motion and Time Class 7 DAV Notes
→ Motion: An object is said to be in motion, if its position changes with time; with respect to a frame of reference. Motion of all kinds is relative in nature.
→ Different Types of Motion
1. Linear Motion: When an object moves along a (nearly) straight line, its motion is called linear motion or rectilinear motion.
2. Circular Motion: When an object moves along a circular or oval path, its motion is called circular motion.
3. Periodic Motion: When the motion of an object is repeated, its motion is called periodic motion.
4. Oscillatory Motion: When an object moves to and fro in relation to a median point, its motion is called oscillatory motion.
5. Rotational Motion: When an object moves on its axis, its motion is called rotational motion. Speed: Speed gives the measure of rate of motion.
Speed = Distance/Time
The SI unit of speed is metre per second (m/s). It is also expressed in other units such as m/minute or km/h.
→ Uniform Motion: When an object moves along a straight path and covers equal distance in equal time, its motion is said to be uniform motion.
→ Non-uniform Motion: When an object covers different distances in equal times, its motion is said to be non-uniform motion.
→ Measurement of Time: Duration of an event is measured in terms of time. The time interval between one sunrise and the next is called a ‘day’. The time taken by the earth to complete one revolution around the sun is called year.
→ Clock: Clock is a device which measures time. Most of the clocks work on simple periodic motion. The motion of a pendulum is an example of simple periodic motion.
→ Simple Pendulum: A simple pendulum is made of a bob which is attached to a taut string The string is fixed to a rigid support. When the bob is at rest, it is at its mean (equilibrium) position. When a pendulum goes from one extreme to another and comes back to first extreme, it completes one oscillation.
→ Time Period of Pendulum: The time taken for one oscillation by the pendulum is known as the time period of the pendulum. The time period of a pendulum of a definite length is constant.
→ Using Graphs to Describe Motion: Distance-Time Graphs
Motion of an object can be shown on a graph. Time is usually shown on the x-axis and distance is usually shown on the y-axis. Following steps need to be followed while plotting a distance-time graph:
- Proper scale should be selected to represent values. The scale should not be too large or too small.
- As per chosen scale, the values for distance and time should be marked on respective axes.
- Points should be marked for given set of values.
- All the points on the graph should be joined.
→ Motion: When an object changes its position with change in time; with reference to a frame of reference, it is said to be in motion.
→ Distance: The total length of the path travelled by an object is called distance.
→ Displacement: The linear distance between starting point and finish point is called displacement.
→ Velocity: Distance covered in unit time is called velocity.
→ Rectilinear motion: When motion happens on a (almost) straight line.
→ Curvilinear motion: When motion happens on a curved path.
→ Periodic motion: When motion of an object is repeated time and again.
→ Simple Periodic Motion: When an object moves to and fro with respect to a fixed median point.
→ Rest: When position of an object does not change with change in time, the object is said to be at rest.
→ Average Speed: Total distance covered divided by total time taken gives the measurement of average speed.