forces, reducing friction

Define force

a push or pull that makes something move

identify the unit for force

Newton, N

identify the effects that forces have on objects

change in motion, acceleration (move faster), deceleration (slower), move in different direction, change in shape

Identify how forces can cause objects to change their motion through non-contact

There is gravity. Gravity can exert a force without touching anything. Gravity is exerting a force on us all the time. Magnets also exert a force on other magnets and some metals without touching them. Electrostatic force is also a non-contact force which can cause charged objects to attract or repel one another

Identify how forces can cause objects to change their motion through contact

Some forces make objects move because of a direct push or pull by another object.

contact forces

The objects must touch each other or be in contact.

non-contact forces

Some forces cause movement without contact or touching.

Describe unbalanced forces

when multiple forces act on an object that are not equal and/or opposite

Describe examples from everyday life of balanced and unbalanced forces

pushing/pulling forces must be equal. If they are, then they cancel out so no movement happens. (balanced)

If they’re not, it will move in the direction of the greater force (unbalanced forces)

Define friction

a force that opposes motion as it prevents two surfaces from sliding over or past one

What is friction and what does it do

Friction is a contact force; two objects have to be touching for friction to work. Can slow down an object or even make it stop.

Describe everyday examples of friction such as walking

There is also friction between our shoes and the floor, so we can walk properly without slipping or sliding

Effects of friction

heat production, wearing away of surfaces and slowing down motion

Describe the wearing away of surfaces from friction

Friction happens when two surfaces rub against each other. The rough parts of the surfaces catch and scrape against each other, causing tiny pieces of material to break off. Over time, this wears the surfaces down. (e.g brake pads rub against the wheels, so friction gradually wears the brake pads down.)

Describe the heat production from friction

Friction produces heat because when two surfaces rub together, their particles collide and vibrate more. This increases the particles’ kinetic energy, which is transferred as thermal energy (heat). (e.g When you rub your hands together, friction makes the particles move more, causing your hands to become warmer.)

Describe the slowing down of motion from friction

Friction is a force that acts in the opposite direction to an object’s motion. This reduces the object’s speed, causing it to slow down and eventually stop. (e.g When you roll a ball across the ground, friction between the ball and the ground acts against its motion, causing the ball to gradually slow down and stop.)

Explain polishing, streamlined bodies and air methods that reduce friction

Polishing – Surfaces are made smoother so there are fewer bumps catching against each other. The force of friction is small for fairly smooth surfaces, like glass or ice. It is much greater for rough surfaces, like sandpaper or concrete.

Streamlined bodies reduce air resistance (drag) by allowing air to flow more smoothly around an object.

Air cushions can separate surfaces so they do not rub directly against each other.

Explain lubricants and ball bearings methods of reducing friction

Lubricants – Oil or grease is added between surfaces to reduce direct contact and make them slide more easily. (e.g oil in an engine)

Ball bearings – Small balls are placed between moving surfaces to change sliding friction into rolling friction, which is smaller. (e.g in bicycle wheels