Physics Chapter: Speed, Light, and Friction

Speed

• Speed is the rate at which an object moves.
• Units of speed include metres per minute, centimetres per second, and kilometres per second
• Seconds per metre is not a unit of speed

Distance, Speed and Time

• The formula for calculating speed is Speed = Distance / Time
• To calculate the time it takes to travel a certain distance, the formula can be rearranged to Time = Distance / Speed

Friction

• Friction is a force that acts between two surfaces in contact.
• Friction can cause objects to slow down.
• Friction can be useful (e.g. allowing us to walk) or a nuisance (e.g. wear and tear on car brakes).
• When friction occurs, energy is converted into heat.

Light

• White light is a mixture of different colours of light.

Primary and Secondary Colours

• Primary colours of light cannot be created by mixing other colours.
• The primary colours of light are red, blue, and green.

Refraction

• When light travels from one medium to another (e.g. from air to water) it bends. This is called refraction.

Potential Energy

• Potential Energy is stored energy.

Kinetic Energy

• Kinetic energy is the energy of motion.

Energy Transformation

• Energy can be transformed from one form to another.
• As a car travels down a slope, gravitational potential energy is converted into kinetic energy.
• Some energy is lost due to friction (e.g. between tyres and the road), which is dissipated as heat energy.

Optical Apparatus

• Common optical apparatus include:
  • Concave lens
  • Convex lens
  • Mirrors
  • Prisms

Concave and Convex Lenses

• Concave lenses are thinner at the centre and thicker at the edges. They cause light to diverge (spread out).
• Convex lenses are thicker at the centre and thinner at the edges. They cause light to converge (focus).

Concave and Convex Mirrors

• Concave mirrors curve inward. They can focus light rays.
• Convex mirrors curve outward. They can diverge light rays.

Uses of Optical Apparatus

• Concave lenses are used in telescopes and some types of glasses.
• Convex lenses are used in magnifying glasses, cameras, and microscopes.
• Mirrors are used in telescopes, reflecting surfaces, and as part of optical instruments.
• Prisms are used to change the direction of light and split white light into its component colors.

Human Eye

• The human eye is a complex organ that allows us to see.
• The components of the eye include:
  • Cornea
  • Iris
  • Pupil
  • Lens
  • Retina.

Functions of the Eye

• The cornea is a transparent, protective outer layer of the eye.
• The iris controls the size of the pupil, which allows light to enter the eye.
• The lens focuses light onto the retina.
• The retina contains light-sensitive cells that convert light into electrical signals that are sent to the brain.

How Light Travels Through the Eye

• Light rays from an object enter the eye and are refracted by the cornea and lens.
• These rays then converge on the retina.

Opaque, Translucent, and Transparent Materials

• Opaque materials do not allow light to pass through them.
• Translucent materials allow some light to pass through them, but the light is scattered so you cannot see clearly through them.
• Transparent materials allow light to pass through them easily, so you can see clearly through them .

Reflection

• When light strikes a surface, it is reflected off the surface.
• The angle of incidence is the angle between the incident ray (incoming ray) and the normal (a line perpendicular to the surface).
• The angle of reflection is the angle between the reflected ray (outgoing ray) and the normal. They always are equal.

Coloured Object and Light

• The colour of an object is observed because some colours of light are absorbed by the object, while others are reflected.
• For example, a red rose reflects red light and absorbs other colours.
• When a yellow light is shone on the red rose, only yellow light is reflected, so the rose appears yellow.
• When a cyan light is shone on the red rose, cyan light is absorbed by the rose, making it look black.
• Green leaves reflect green light and absorb other colours.
• When a yellow light is shone on green leaves, the green light is absorbed, and the rose appears black.
• When a cyan light is shone on green leaves, the leaves appear green.

This quiz covers essential concepts from physics, focusing on speed, distance, time, friction, and light. You'll explore the relationships between these topics and how they interact in various scenarios. Perfect for reinforcing your understanding of basic physical principles.