A force is often defined as a "push" or a "pull". There is nothing untrue with this statement, but does not really tell you much about a force. Instead of defining force, it substitutes an antonym. A physicist prefers to define a force in terms of what it does.
Introduction to forces:
Just what does a force do? Suppose you squeeze a balloon without breaking it. The obvious result is that you change its shape. If you kick a ball it starts moving. A moving body can be brought to rest by application of a force. Force is invariably connected to motion in physics. Or the direction of speed of a moving body can be changed by application of a force.
The effect of unbalanced and balanced forces on a ball
We can define force as follows:
Force is that physical quantity which changes or tends to change a body's state of rest or of uniform motion in a straight line.
An unbalanced force changes the state of constant velocity including zero velocity of a body on which it acts. Forces may be balanced or unbalanced. An iron ball suspended from a hook by a wire [Figure (a) shown below] has two forces acting on it, its weight, acting vertically downward and the tension acting on the wire vertically upward. Since these forces are equal in magnitude and opposite in direction, their resultant is zero. Figure (b) and (c) below show that when the resultant of a group of forces acting on the same object is zero, the forces are balanced. When the resultant is not equal to zero, the resultant is an unbalanced force.
When the resultant of a group of forces acting on the same object is zero, the forces are balanced. When the resultant is not equal to zero, the resultant is an unbalanced force.
Resultant of a group of forces acting on the same object is zero, the forces are balanced. When the resultant is not equal to zero, the resultant is an unbalanced force.
In our daily life we come across many kinds of mechanical forces such as pull, push, squeeze, stretch etc. Pictures shown below explain the action of some of the above forces.
Force may be (a) push or (b) pull
If a girl pushes a pram she feels the force exerted by her muscles which became taut. [Figure (a) above]. A boy throwing a cricket ball feels a force in the same way. When a tug uses a strong rope to pull a boat from a sand bank the rope becomes taut [Figure (b) shown above].
Examples of contact forces are frictional forces, normal reaction forces, tensions and forces in collisions. Forces at a distance (non-contact forces) include gravitational forces of attraction between two masses, electrical forces of attraction between two masses, electrical forces of attraction (or repulsion) between two electrically charged objects and magnetic forces of attraction (or repulsion) between two magnetised objects or a magnetised object and a magnetic material.
Forces at a distance
Forces are described in different names. Some forces are shown in the following diagram [Figure (a) shown below]. A weight is the pulling force due to gravity which always acts vertically downwards.
The weight of an object is measured using a spring balance. The spring balance consists of a spring enclosed in a casing, fixed at one end. A pointer moves along a suitably calibrated scale alongside. There is a hanger which can be used to suspend the balance and a hook on which to hang the object to be weighed. The force registered by the pointer is the weight of the object.
A tension is the force in a rope or chain as shown in the diagram.
A reaction is the force of a surface on an object resting against it. In [Figure (b) shown above] the ladder rests against a part of the wall which is smooth, the total reaction is perpendicular (normal) to the wall as shown. But to prevent the ladder from slipping, a frictional force must act as the ground.
Some of the forces that occur in nature are:
Introduction to forces:
Just what does a force do? Suppose you squeeze a balloon without breaking it. The obvious result is that you change its shape. If you kick a ball it starts moving. A moving body can be brought to rest by application of a force. Force is invariably connected to motion in physics. Or the direction of speed of a moving body can be changed by application of a force.
We can define force as follows:
Force is that physical quantity which changes or tends to change a body's state of rest or of uniform motion in a straight line.
An unbalanced force changes the state of constant velocity including zero velocity of a body on which it acts. Forces may be balanced or unbalanced. An iron ball suspended from a hook by a wire [Figure (a) shown below] has two forces acting on it, its weight, acting vertically downward and the tension acting on the wire vertically upward. Since these forces are equal in magnitude and opposite in direction, their resultant is zero. Figure (b) and (c) below show that when the resultant of a group of forces acting on the same object is zero, the forces are balanced. When the resultant is not equal to zero, the resultant is an unbalanced force.
When the resultant of a group of forces acting on the same object is zero, the forces are balanced. When the resultant is not equal to zero, the resultant is an unbalanced force.
Resultant of a group of forces acting on the same object is zero, the forces are balanced. When the resultant is not equal to zero, the resultant is an unbalanced force.
If a girl pushes a pram she feels the force exerted by her muscles which became taut. [Figure (a) above]. A boy throwing a cricket ball feels a force in the same way. When a tug uses a strong rope to pull a boat from a sand bank the rope becomes taut [Figure (b) shown above].
Examples of contact forces are frictional forces, normal reaction forces, tensions and forces in collisions. Forces at a distance (non-contact forces) include gravitational forces of attraction between two masses, electrical forces of attraction between two masses, electrical forces of attraction (or repulsion) between two electrically charged objects and magnetic forces of attraction (or repulsion) between two magnetised objects or a magnetised object and a magnetic material.
Forces at a distance
- Are equal and opposite.
- Depend upon the distance between the two objects.
- Depend upon the medium between the two objects for electrical and magnetic
Forces are described in different names. Some forces are shown in the following diagram [Figure (a) shown below]. A weight is the pulling force due to gravity which always acts vertically downwards.
The weight of an object is measured using a spring balance. The spring balance consists of a spring enclosed in a casing, fixed at one end. A pointer moves along a suitably calibrated scale alongside. There is a hanger which can be used to suspend the balance and a hook on which to hang the object to be weighed. The force registered by the pointer is the weight of the object.
A reaction is the force of a surface on an object resting against it. In [Figure (b) shown above] the ladder rests against a part of the wall which is smooth, the total reaction is perpendicular (normal) to the wall as shown. But to prevent the ladder from slipping, a frictional force must act as the ground.
Some of the forces that occur in nature are:
- Gravitational force
- Nuclear force
- Magnetic force of attraction and repulsion.
- Electrical force of attraction or repulsion
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