Force:
A push or pull that changes the position, size, shape and speed of the moving body is called force. It can also change the direction of the moving body. Force is measured in terms of newton.
| Force can |
| change the states of the body from movement to rest |
| change the states of the body from rest to movement |
| alter the speed of the object |
| change the shape of the object |
| change the direction of the movement of the object |
By observing the motion of a marble on an inclined plane, Galileo Galilei concluded that objects constantly move when no force acts on them .
Case 1:
If the planes' inclinations on both surfaces are equal, the marble will climb the same distance as it covers while rolling down.
If the planes' inclinations on both surfaces are equal, the marble will climb the same distance as it covers while rolling down.
Case 2:
When the angle of inclination of the right-side plane slowly decreased, the marble would travel farther distance until it reaches the original height.
Case 3:
When the right-side plane is made horizontal, the marble will continue to move forever, trying to reach the same height where it was released from.
Thus, by observing all three cases, Galileo concluded that the unbalanced external force must change the marble's motion, however no net force is required to keep the object in uniform motion.
Balanced forces - equal in strength and opposite in direction, resulting in no net change in the object's motion.
Unbalanced forces - unequal, causing a change in the object's motion, such as acceleration or a change in direction.
Newtons first law of motion
An object remains in a state of rest or uniform motion in a straight line unless an external force acts on it.
Inertia:
The body's tendency to oppose the change in its state of rest or uniform motion in a straight line is called inertia. Newton's first law of motion is also called the law of inertia.
Mass:
The inertia of a body depends upon mass. We know it is not easy to move a heavier object than the lighter one.
Types of inertia:
- Inertia of rest
- Inertia of motion
- Inertia of direction
Momentum
The product of mass, (m) and velocity, (v) gives the momentum, (p). That is,
\(p\ =\ m v\)
The SI unit is kilogram metre per second \(kg\ m s^{–1}\), and it is a vector quantity
Newton's second law of motion
The rate of change of momentum (acceleration) of an object is directly proportional to the applied unbalanced force in the same direction of force and inversely proportional to the mass of the object.
\(F\ \propto\ \frac{m\ \times\ (v−u)}{t}\)
\(F\ =\ \frac{k\ m\ \times\ (v−u)}{t}\)
Where \(k\) is the constant of proportionality.
\(F\ =\ ma\),
\(a\ =\ \frac{v\ -\ u}{t}\)
Newton's third law of motion
The third law of motion generally states that "For every action, there is always an equal and opposite reaction". The forces never act on the same object but different objects.
Law of conservation of momentum
In the absence of unbalanced external force, the sum of momenta of the two objects before and after the collision will be equal. Or, the total momentum of the two objects is unchanged or conserved by the collision.
\(m_A\ u_A\ +\ m_B\ u_B\ =\ m_A\ v_A\ +\ m_B\ v_B\)