# Forces and Motion: Forces and Friction

## Forces and Motion: Forces and Friction

• Forces are pushes or pulls that can change the motion of an object. They can alter the speed, the direction, or the shape of the object.

• Frictional force is a force that opposes the motion of an object. It is caused by the interaction between two surfaces attempting to slide past each other.

• Friction has beneficial effects such as allowing us to walk without slipping and enabling car tyres to grip the road.

• However, it can also be unfavourable. For example, it leads to wear and tear on machinery and other tools, requiring maintenance and repair.

• There are different types of friction: static, sliding, rolling, and fluid friction (also known as air or water resistance).

• The force of friction depends on the nature of the surfaces involved and how hard they are pushed together.

• The contact force is another vital concept, it is created when two objects come into contact with each other.

• When forces are balanced, they result in stationary objects, or objects moving at a steady speed in a straight line. When forces are unbalanced, this results in an acceleration (change in speed or direction).

• Lubrication reduces friction by creating a thin layer between two surfaces, allowing them to slide more easily over each other.

• The resistance of an object to motion, due to friction or any other force, is known as inertia.

• Newton’s first law states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. This is sometimes referred to as the law of inertia.

• Newton’s second law establishes a direct proportionality between resultant force and the change in motion, and an inverse proportionality between the mass of an object and the change in motion.

• Newton’s third law states that for every action, there is an equal and opposite reaction.

• Other forces that can also affect motion include gravitational force, magnetic force, and electrostatic force.

• Remember that all objects have a centre of mass - the point at which the weight of the object can be considered to be concentrated.

• Work done on an object is defined as the force applied to the object multiplied by the distance the object moves in the direction of the force - work done = force x distance.

• Knowledge of forces, friction and associated principles is fundamental in understanding more complex topics in Physics, such as energy transfer, momentum, electricity, and thermodynamics.