First Law of Motion

         From the observation of motion on the sloping surface of objects, Galileo concluded that objects move at a constant speed unless an external force is felt.

        He observed that the velocity increases when the lakhoti falls on a sloping surface (Figure (a)).  Now in the next  you will learn that Lakhoti moves downwards due to unbalanced gravitational force and achieves a certain momentum till it reaches the bottom.  As shown in Figure (b), the speed decreases when the lakhoti moves upwards.  As shown in Figure (c), a lakhoti is stationary on a non-frictional ideal flat sloping surface on both sides.

       Galileo argued that when Lakhoti is released from the left, it falls down the slope and reaches the same height on the right slope as it is released from.  If the slopes of the plane on both sides are the same, Lakhoti will reach the same height as it falls from the height.  If the slope of the right-hand slope is gradually reduced, the lakhoti will have to cut a greater distance to achieve the same height.

      Now if the plane on the right is made horizontal (i.e. the slope is reduced to zero, then Lakhoti will continue to move continuously on the horizontal plane to achieve the original height.  Unbalanced (external) force is required to change; but no consequential force is required to keep Lakhoti's steady motion.

       In practical conditions it is difficult to achieve zero unbalanced force. After cutting the gap, it becomes stable. To reduce the effect of friction, smooth and smooth surface should be used and lubricant should be applied on the surface.

       Newton further studied Galileo's ideas about force as well as motion and introduced three basic laws explaining the motion of a moving object.  These three laws are known as Newton's laws of motion.  

The first law of motion is as follows: 

"Everything maintains its steady state or steady state of motion on a straight path unless it is forced to change position by some external force."

    In other words, everything opposes the change in its state of motion.  Inertia is the nature of an object being in a state of constant motion or motion at a constant speed.  For the same reason the first law of motion is also called the law of inertia.  

      Experiences while traveling in a motorcar can be described by the law of inertia.  Relative to the seat we remain stationary until the driver applies the brakes to stop the motorcar.  Applying the brakes also brings the seat along with the car to a stable position;  But our body tends to be in motion due to inertia.  Sudden braking can injure us by colliding with the front panel of the seat.  Using safety belts to prevent this type of accident.

       The safety belts exerts a force that slows down the forward movement of our body.  The opposite experience happens to us when we are standing in the bus and the bus starts suddenly.  In this position we lean backwards.  The reason for this is that when the bus suddenly turns, our feet that are in contact with the bottom of the bus come into motion;  But the upper part of the body resists this motion due to inertia.  When a motorist takes a sharp turn very fast, we lean to one side.  This fact can be understood from the law of inertia.  Our body keeps moving on a straight path when an unbalanced force is applied by the engine to change the direction of the motorcar while our body bends to one side on the seat due to inertia.  The fact that an object remains stationary as long as there is no unbalanced force can be illustrated by the following activities:  

Activity:-

      Hit another cooker or striker with your fingers in the horizontal direction and hit the bottom cooker of the pile.  If you hit the cooker with enough intensity you will see that only after coming out of the bottom cooker the rest of the cookers come in a downward direction due to inertia without changing their alignment.