# Forces and their Effects

Section: Forces and Their Effects

• Force: A push, pull or twist that can change an object’s shape or motion. It is measured in Newtons (N).

• Balanced and Unbalanced Forces: If forces act equal in size but opposite in direction, they are balanced which means no change in motion. If forces are unequal, they are unbalanced, causing change in speed or direction of an object.

• Contact and Non-contact Forces: Contact forces act between two objects in physical contact (e.g., friction, tension), while non-contact forces act over a distance (e.g., gravitational, electric and magnetic forces).

• Friction: A force that opposes motion between two surfaces that are in contact with each other. Friction can be reduced by lubrication or making surfaces smoother.

• Air Resistance or Drag: The force opposing the motion of an object moving through air. It increases with the speed of the object, its size and shape.

• Weight: The force on an object due to gravity. Calculated by multiplying the mass of an object by the gravitational field strength (Weight = Mass x Gravitational field strength).

• Mass: The amount of matter in an object, measured in kilogrammes.

• Gravitational Field Strength: On earth, it is approximately 10 N/kg.

• Effects of Forces: Forces can cause an object to start moving, stop moving, speed up, slow down, change direction or change shape.

• Newton’s First Law: An object will remain at rest or in uniform motion in a straight line unless acted upon by an external force.

• Newton’s Second Law: The acceleration of an object is directly proportional to the force applied and inversely proportional to its mass (Force = mass x acceleration).

• Newton’s Third Law: For every action, there is an equal and opposite reaction.

• Inertia: The resistance of an object to change in its state of motion. It is directly proportional to the mass of the object.

• Resultant Force: The combination of all the forces acting on an object. If the resultant force on an object is zero, it will either remain still or keep moving at the same speed in the same direction. If there is a resultant force, the object will accelerate or decelerate.

Remember to work through numerous example problems to apply the concepts of Newton’s Laws and forces to real-world situations.