Forces Between Bodies

Forces Between Bodies

Understanding Forces

• A force is a push, pull, or twist that can cause an object to accelerate, decelerate, change its direction or shape.
• It is measured in newtons (N) and is a vector quantity, which means it has both magnitude (size) and direction.
• The forces on an object can be represented using force diagrams (also known as free-body diagrams).

Contact and Non-Contact Forces

• Contact forces are the forces that act between two bodies in contact. Types of contact forces include friction, tension, normal force and air resistance.
• Non-contact forces are the forces that act on an object without touching it. Examples include gravity (weight), electrostatic and magnetic forces.

Balanced and Unbalanced Forces

• If the resultant force (or net force) on an object is zero, we say the forces are balanced. In this case, the object will continue in its current state of motion – either staying at rest or moving with constant velocity.
• If the resultant force on an object is not zero, we say the forces are unbalanced. An unbalanced force will cause the object to accelerate in the direction of the resultant force.

Friction and Air Resistance

• Friction is a force that opposes motion. It acts between two surfaces that are in contact and moving past each other.
• Air resistance is a type of friction that acts on objects moving through air. It increases with the speed of the object and the surface area facing the oncoming air.

Weight and Gravitational Force

• An object’s weight is the force acting on it due to gravity. It is calculated as the mass of the object multiplied by gravitational field strength (w = m * g).
• Weight is different from mass: weight is a force and depends on the local value of gravity, while mass is a measure of the amount of material in an object and is the same everywhere.

Tension and Compression

• The tension force is a pulling force exerted by a string, cable, chain, etc. when it is stretched. It acts along the length of the object and away from any object attached to it.
• Compression is a squeezing force that can change the shape or volume of an object, or even cause it to break apart.

Normal Force

• The normal force (or reaction force) is the support force exerted upon an object that is in contact with a stable object. For example, it is the force that prevents an object from falling through the ground.

Centripetal Force

• The centripetal force is the force that keeps an object moving in a circular path. It always points towards the centre of the circle. An example is the tension in a string when whirling an object around.