Haryana State Board HBSE 9th Class Science Notes Chapter 8 Motion Notes.
Haryana Board 9th Class Science Notes Chapter 8 Motion
→ The change in position is a motion.
→ The motion may be defined in terms of distance covered or displacement.
→ All living things, whether they are plants or animals, do some type of motion.
→ It is easy to describe the motion of animals as compared to plants.
→ Any external factor is required for the movement of non-living things.
→ Distance is a scalar quantity.
→ Displacement is a vector quantity.
→ SI unit of speed is metre per second (ms-1). Other units are centimetre per second (cms-1) and kilometre per hour (kmh-1).
→ If an object covers a distance s in time t, then its speed (v) will be:
v = \(\frac{s}{t}\)
→ The speed of sound in air is 346 ms-1.
→ If the acceleration is in the direction of velocity, then it is taken as +ve, and if it is in the opposite direction to that of the velocity, then it is taken as -ve.
→ The SI unit of acceleration is metre per second square (ms-2).
→ The motion of a freely falling body is an example of uniformly accelerated motion.
→ In distance-time graph, the time is taken on X-axis and distance is taken on Y-axis.
→ For a uniform speed, the graph of the distance covered with respect to time is a straight line.
→ The change in the velocity of a body with time, moving in a straight line is shown by velocity-time graph.
→ In velocity-time graph, the time is taken on X-axis and velocity is taken on Y-axis.
→ The motion of a body moving with uniform acceleration may be defined by three equations. These are:
- v = u + at
- s = ut + \(\frac{1}{2}\) at2
- 2as = v2 – u2
→ If an athelete takes a time, t seconds to move around a circular path of radius r, then velocity
→ Speed: The distance travelled by the body per unit time is known as its speed.
→ Velocity: The displacement per unit time is known as the velocity of the body.
→ Distance: The actual path travelled by any body is known as distance.
→ Displacement: The shortest distance between the initial and final position of the body is called displacement.
→ Origin Point: We require a reference point to show the position of any body, which is called origin point.
→ Uniform Motion: Motion of a body is said to be uniform, if it covers equal distances in equal intervals of time.
→ Non-uniform Motion: Motion of a body is said to be non-uniform, if it covers unequal distances in equal intervals of time.
→ Average Speed: The ratio of the total distance travelled by any body to the total time.
∴ Average speed v = \(\frac{\text { Total distance travelled }(s)}{\text { Total time }(t)}\)
→ Average Velocity: If the velocity of any body changes equally, then the arithmetic mean of initial and final velocity is known as average velocity.
∴ Average velocity (vav) = \(\frac{\text { Initial velocity }(\mathrm{u})+\text { Final velocity }(\mathrm{v})}{2}/latex]
→ Acceleration: The time rate of change of velocity of a moving body is called acceleration.
Change in velocity (v – u)
∴ Acceleration (a) = [latex]\frac{\text { Change in velocity }(\mathrm{v}-\mathrm{u})}{\text { Time taken }(\mathrm{t})}\)
Time taken (t)
→ Uniform Acceleration: A body is said to be moving with uniform acceleration, if there is equal change in velocity in equal interval of time.
→ Non-uniform Acceleration: If the velocity of any body changes non-uniformly, then that is known as non-uniform acceleration.
→ Uniform Circular Motion: When a body moves in a circular path with uniform speed, its motion is called uniform circular motion.