Laws of Motion Concept Page - 1

Example

Addition and Subtraction of Forces

For the block A, the net force acting is F1+F2. The two forces are added.
For the block B, the net force acting is F1−F2. The two forces are subtracted.

Definition

Units of Force

The unit of force in MKS system is newton (N)
1N=1kg×ms2
The unit of force in CGS system is dyne
1 Newton = 105 dynes

Example

Addition and Subtraction of Forces

Definition

Calculation of net force from given velocity time graph

A block of mass 12 kg  is hanging with a light string in a lift as shown in the figure (a). The lift is moving in upward direction and its speed time graph is plotted as shown in the figure (b) : (take g=10m/s2):
In the time interval t=0 to t=5, the acceleration a=10−05−0=2m/s2
  Hence T=m(g+a)
  T=12×(10+2)=144N
In the time interval t=5 to t=10, the acceleration a=0
    Hence T=mg=12×10=120N
In the time interval t=10 to t=15, the acceleration a=30−1015−10=4m/s2
    Hence T=m(g+a)
               T=12×(10+4)=168N

Example

Force changes direction of motion

When a ball hits against a wall, it bounces back in the opposite direction. So the force exerted by the wall on the ball changes its direction of motion.

Example

Force changes shape of object

When a hammer strikes a hot rod, the rod bends. The force exerted by the hammer on the rod changes the shape of the rod.

Example

Force can change the speed of an object

Blowing wind or wind storm can change the speed of moving car.

Example

Force can change the direction of an object

A side wind can change the direction of a boat sailing in a sea.

Example

Examples for effect of force

Force may bring the following change:
1) Can change the state of an object(rest to motion/ motion to rest):For example, pushing a heavy stone in order to move it.
2) May change the speed of an object if it is already moving.For example,catching a ball hit by a batsman.
3) May change the direction of motion of an object.For example,footballer kicks a   moving ball to change its direction.
4) May bring about a change in the shape of an object.For example, blowing air in balloon.
5) May cause some or all of these effects.

Definition

Balanced and Unbalanced Forces

Balanced force:Forces acting on an object which does not change the state of rest or of uniform motion of it are called balanced forces.

Unbalanced force:The resultant of two opposite forces acts on an object and brings it in motion. These opposite forces are called unbalanced forces.

BookMarks

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