From the smartphone in your pocket to the rockets launching satellites into orbit, waves and motion principles are at the heart of modern technology. In this lesson you will explore how Newton's laws power transport, how electromagnetic waves enable global communication, and how wave properties are harnessed for medical imaging. You will also learn to evaluate technologies using scientific evidence.
Think about the technologies you use every day — your phone, a car, medical scans.
Write down your answers before reading on:
Cars, planes and rockets — powered by Newton's laws
Every vehicle you see on the road, in the air or in space relies on Newton's laws of motion. Understanding these laws helps engineers design safer, faster and more efficient transport.
First law: A stationary car stays still until the engine provides a force through the wheels. A moving car keeps moving until friction and braking forces slow it down. Seatbelts are designed specifically to counteract inertia — when a car stops suddenly, the occupants would keep moving forward at the car's original speed unless restrained.
Second law (F = ma): The acceleration of a car depends on the net force from the engine and the mass of the car. A more powerful engine (greater force) or a lighter car (less mass) produces greater acceleration. This is why racing cars are built from lightweight carbon fibre.
Third law: The tyres push backward on the road, and the road pushes forward on the tyres with an equal and opposite force. Without this action-reaction pair, a car could not accelerate.
Newton's third law also explains how planes fly. Wings are shaped so that air is deflected downward as the plane moves forward. The wing pushes air down (action), and the air pushes the wing up (reaction) — this upward force is called lift. The engines provide forward thrust, while drag and gravity oppose the motion.
Rockets do not push against the ground or the air to move. Instead, they expel hot gases downward at high speed. The rocket pushes exhaust gases out (action), and the exhaust gases push the rocket upward (reaction). This is why a rocket works in the vacuum of space — it does not need a medium to push against.
Mobile phones, WiFi and satellites — using electromagnetic waves
Modern communication relies on electromagnetic (EM) waves because they can travel through a vacuum and carry information over enormous distances at the speed of light (approximately 300 000 km/s).
Your phone converts your voice or message into an electrical signal, which is then encoded onto a radio wave and transmitted to the nearest mobile tower. The tower receives the signal and sends it through a network of cables and other towers until it reaches the recipient's phone. Different carriers use different frequency bands within the radio and microwave regions of the EM spectrum.
WiFi uses radio waves (typically 2.4 GHz or 5 GHz) to send data between devices and a router. Like all EM waves, WiFi can pass through walls and ceilings — though thicker or denser materials weaken the signal. The higher the frequency, the more data can be carried, but the shorter the effective range.
Communication satellites orbit Earth and relay signals between distant locations. A signal is sent from the ground to the satellite using microwaves, the satellite amplifies it and retransmits it back to another ground station. Because microwaves can penetrate clouds and rain better than some other EM waves, they are ideal for satellite communication. Australia's vast distances make satellite communication especially important for remote communities.
Ultrasound, X-ray and MRI — seeing inside the body with waves
Medical imaging technologies use different types of waves to create pictures of the inside of the human body without surgery. Each technology uses wave properties in a different way and has different strengths and limitations.
Ultrasound uses high-frequency sound waves (above 20 000 Hz, beyond human hearing). A transducer sends pulses of ultrasound into the body. When these sound waves meet a boundary between tissues of different density, some of the wave is reflected back as an echo. The transducer detects these echoes, and a computer uses the time delay to build an image.
Ultrasound is safe, relatively cheap and does not use ionising radiation. It is commonly used to monitor pregnancies and examine organs such as the heart and kidneys. However, ultrasound cannot pass effectively through bone or air, so it is not useful for imaging the brain or lungs.
X-rays are high-energy electromagnetic waves. They pass easily through soft tissue but are absorbed by denser materials such as bone. When X-rays pass through the body and strike a detector on the other side, the shadow image reveals the structure of bones and dense organs.
X-rays are fast and excellent for detecting fractures and dental problems. However, X-rays are a form of ionising radiation, which means they can damage living cells. Exposure is therefore kept as low as reasonably possible, and lead aprons are used to shield parts of the body not being imaged.
MRI does not use ionising radiation or sound waves. Instead, it uses strong magnetic fields and radio waves. The magnetic field aligns hydrogen atoms in the body. Radio waves are then pulsed through, disturbing this alignment. When the radio waves stop, the hydrogen atoms return to their original alignment and emit their own radio signals. A computer processes these signals to create detailed images of soft tissues, including the brain, muscles and ligaments.
MRI produces highly detailed images and is especially useful for brain and spinal cord conditions. However, MRI machines are expensive, require specialised facilities, and cannot be used with patients who have certain metal implants.
| Technology | Wave type | Key strength | Key limitation |
|---|---|---|---|
| Ultrasound | High-frequency sound | Safe, no radiation, real-time imaging | Cannot pass through bone or air |
| X-ray | High-energy EM wave | Fast, excellent for bone imaging | Ionising radiation risk |
| MRI | Radio waves + magnetic field | Detailed soft-tissue images | Expensive, not suitable with some implants |
Using evidence to assess wave and motion technologies
Scientists and engineers evaluate technologies by comparing them against clear criteria using reliable evidence. When evaluating technologies that use waves or motion principles, important criteria include:
"Rockets push against the ground or air to move." No — rockets work in the vacuum of space by expelling exhaust gases downward (action). The exhaust gases push the rocket upward (reaction). Newton's third law explains propulsion without any medium to push against.
"X-rays and MRI use the same type of waves." No — X-rays use high-energy electromagnetic waves that ionise tissue. MRI uses magnetic fields and low-energy radio waves. They are completely different technologies with different risks and applications.
National Broadband Network (NBN): Australia's NBN uses a mix of fibre-optic cables, fixed wireless and satellite technology to deliver internet across the country. Satellite services (Sky Muster) are essential for remote and rural communities where cables are impractical. These satellites use microwaves to relay data between ground stations and homes across the outback.
Royal Flying Doctor Service: This iconic Australian service uses radio and satellite communication to coordinate emergency medical flights across vast distances. Electromagnetic waves enable rapid communication between remote locations and medical centres, saving lives in areas where other infrastructure is limited.
Australian Space Agency: Founded in 2018, the Australian Space Agency supports satellite development, Earth observation and space research. Satellites launched by Australian and international partners use Newton's laws for orbital motion and electromagnetic waves for data transmission back to Earth.
1. Which of Newton's laws best explains how a rocket accelerates in space?
2. Why are electromagnetic waves ideal for satellite communication?
3. A doctor needs to check the heartbeat of a developing fetus. Which technology is most appropriate?
4. Which statement correctly compares X-ray and MRI imaging?
5. A remote community in outback Australia needs a reliable imaging service. Which criterion is MOST important when evaluating options, and which technology best meets it?
1. Explain how Newton's three laws of motion apply to the design and safety features of a modern car. Include at least one safety feature and explain which law it relates to. 4 MARKS
2. Compare how mobile phones and satellites use electromagnetic waves for communication. In your answer, explain why electromagnetic waves are used rather than sound waves. 4 MARKS
3. Evaluate the use of ultrasound, X-ray and MRI for medical imaging in rural Australia. Discuss at least two criteria (for example: safety, cost, accessibility, accuracy) and explain which technology best meets the needs of remote communities. 4 MARKS
Go back to your Think First answer. Has your understanding changed?
C — Newton's third law explains rocket propulsion. The rocket pushes exhaust gases downward (action), and the exhaust gases push the rocket upward with an equal and opposite force (reaction). This works even in the vacuum of space because the action-reaction pair involves the rocket and its exhaust, not the rocket and the surrounding medium.
B — Electromagnetic waves are ideal for satellite communication because they can travel through a vacuum at the speed of light. Sound waves are mechanical waves that require a medium and cannot travel through the empty space between a satellite and Earth.
A — Ultrasound is the most appropriate for checking a developing fetus because it uses sound waves and does not use ionising radiation. X-rays use ionising radiation and are avoided during pregnancy unless absolutely necessary. MRI is not typically the first choice for routine fetal checks.
D — X-ray uses high-energy electromagnetic waves that pass through soft tissue but are absorbed by bone. MRI uses strong magnetic fields and radio waves to create detailed images of soft tissues. They use completely different physical principles and have different strengths.
B — For a remote community, portability and accessibility are the most important criteria. Ultrasound machines are relatively inexpensive, portable and do not require specialised facilities or shielding. MRI machines are large, expensive and immobile. X-ray machines also require shielding and trained operators.
Model answer: Newton's first law explains why seatbelts are necessary — when a car brakes, passengers continue moving forward due to inertia unless restrained. Newton's second law (F = ma) shows that a more powerful engine or lighter car produces greater acceleration. Newton's third law explains traction: tyres push backward on the road, and the road pushes the car forward. Airbags are another safety feature linked to the first law — they extend the stopping time for the head, reducing the force experienced (also connected to F = ma, since reducing acceleration reduces force).
Model answer: Mobile phones transmit signals as radio waves to nearby towers, which relay the signal through networks. Satellites use microwaves to communicate with ground stations across vast distances, including over oceans and remote areas. Electromagnetic waves are used rather than sound waves because EM waves can travel through a vacuum at the speed of light, carry large amounts of data, and are not blocked by the absence of a medium. Sound waves are mechanical waves that need a material medium and would be completely unable to travel between Earth and satellites.
Model answer: For rural Australia, cost and accessibility are critical criteria. Ultrasound is relatively inexpensive, highly portable and safe, making it ideal for remote clinics and the Royal Flying Doctor Service. X-ray is useful for diagnosing fractures but requires shielding and carries a small radiation risk. MRI provides the most detailed soft-tissue images but is extremely expensive, requires a specialised facility and is usually only available in major cities. Therefore, ultrasound best meets the needs of remote communities because it balances effectiveness, safety and accessibility. However, patients needing MRI may still need to travel to regional centres, highlighting an equity issue in healthcare access.
Jump through the tech world and test your knowledge! Scale platforms, dodge obstacles and answer questions about waves and motion in technology to boost your score.
Tick when you have finished all activities and checked your answers.