Samacheer Class 7 Science - Force and Motion

An object moving in uniform circular motion is moving around the perimeter of the circle with a constant speed. While the speed of object is constant, its velocity is changing, Ex: Merry-go-round, roller coaster, planets orbiting the sun.

There are two possible answers:
Velocity gives an idea of how fast the position changes, or Acceleration gives an idea of how fast the velocity changes.

A body is said to have constant acceleration, if it travels is a straight line and its velocity increases or decreases by equal magnitude in equal intervals of time.
Ex: the motion of a freely falling body.

Stability is a measure of the body’s ability to maintain its original position.
The three types of stability are
Stable equilibrium
Unstable equilibrium
Neutral equilibrium
Stable Equilibrium:
The frustum can be tilted through quite a big angle without toppling.

Its centre of gravity is raised when it is displaced. The vertical line through its centre of gravity still falls within its base. So it can return to its originalposition.
Unstable Equilibrium:
The frustum will topple with the slightest tilting. Its centre of gravity is lowered when it is displaced.

The vertical line through its centre of gravity falls outside its base.

Neutral Equilibrium:
It causes frustum to topple.
The frustum will roll about but does not topple.
Its centre of gravity remains at the same height when it is displaced.
The body will stay in any position to which it has been displaced.

Make three holes in the lamina.
Suspend the lamina from the optical pin through one of the holes

Suspend the plumb line from the pin and mark the position of the plumb line on the lamina’
Draw lines on the lamina representing the positions of the plumb line.
Repeat the above steps for the holes.
Label the intersection of the three lines as X, the position of the center of gravity of the lamina.

Given : time taken = 15 minutes [1 min = 60 sec]
= 15 x 60 = 900 sec
Speed – 2 m/s
Distance = ?
Formula : Distance = Speed x time = 2 x 900
Distance between her house and the school = 1,800 m

Given :
Initial velocity of the car (u) = 0 m/s
Final velocity of the car (v) = 20 m/s
time taken = 10s
Acceleration = ?
Formula: Acceleration = \(\frac { 20 – 0 }{ 10 }\) = \(\frac { 20 }{ 10 }\)
Acceleration of the car = 2 m/s2

Distance : 17
Distance: 24
Displacement: 3
Displacement: 1
When the rabbit moves in a straight line from A to B, the distance and displacement will be equal.

(ii) Usain Bolt covers 100 m distance in 9.58 seconds. Calculate his speed. Who will be the winner if Usain Bolt comepetes with a Cheetah running at a speed of 30 m/s

(iii) You are walking along east covering a distance of 4 m, then 2 m towards south, then 4 m towards west and at last 2 m towards north. You cover the total distance in 21 seconds, what is your average speed and average velocity?
Total distance covered = 12 m
Total time taken =21 seconds

\(\frac { 12m }{ 21 }\) = 0.571 m/s
Average velocity = 0 m/s
Average velocity is zero because the starting point and the finishing point is same
∴Displacement is zero so, average velocity is also

When the velocity of the object is decreasing by 20m/s the deceleration is 20 m/s2.

The velocity of the object is decreasing by 20m/s in one second.