Force is defined as a push or pull that can cause an object's motion to change. It is measured in Newtons (N), with 1N being the force needed to accelerate 1kg of mass by 1m/s^2. There are two main types of forces - contact forces like friction and tension which require touching objects, and action-at-a-distance forces like gravity and magnetism which act without direct contact. Force is a vector quantity that has both magnitude and direction.

1. What is Force? 1) Force is a push or pull 2) Force is the capacity to do work or cause physical change 3) Force= Mass times acceleration (F = ma) 4) A force is that which changes or tends to change the state of rest or motion of a body.

2. GROUPS OF FORCES: A. Contact Forces : 1. frictional force (friction)- caused by the rubbing of two objects.

3. 2. buoyant force (buoyancy)- it is the upward force of fluids on floating objects. 3. normal force- is the support force on an object which is in contact with another stable object. 4. air resistance force - type of frictional force upon objects as they travel through the air.

4. 5. Tension force - is the pulling force through a string, rope, cable or wire. 6. Spring force - is the force exerted by a compressed or stretched spring upon any object which is attached to it . 7. Applied force - is a force which is made to an object by a person or another object.

5. B. Action-at-a-distance forces : 1. gravitation- is the force with which the earth, moon, or other very large object attracts another object towards itself. 2. Electrostatic force – is the force between particles that are caused by their electric charges. Electric force - 3.magnetic forces – is the force made between magnetic poles

6. Common Units of Force --->> SI : Newton (N) 1 N = 0.225 lb; One Newton (N) of force is defined as the amount of force needed to accelerate 1 kilogram (kg) of mass at a rate of 1 meter per second squared (m/s2). 1 Newton = 1 kg m/sec2 (A kilogram is the amount of weight at which 1 N of force will accelerate at a rate of 1 m/s2.)

7. A force is a vector quantity . A vector quantity is a quantity which has both magnitude and direction. Example: 10 Newtons, downwards 25 km, east A scalar quantity can be described using only 1 quantity, magnitude. Examples: time, energy, volume, temperature.