Principles of the Physical World: Senior Cycle Physics · 5th Year · Mechanics and the Laws of Motion · Autumn Term

Changes in Speed: Getting Faster and Slower

Students will observe and describe objects getting faster (speeding up) or slower (slowing down) in everyday situations.

• NCCA Curriculum Specifications
• NCCA: Primary Curriculum - Science - Energy and Forces

About This Topic

Changes in speed occur when objects accelerate or decelerate due to unbalanced forces. Students observe a ball speeding up as it rolls down a hill from gravity's pull, or a toy car slowing on carpet from friction. This topic builds descriptive skills for everyday motion, fitting the Mechanics and Laws of Motion unit in Senior Cycle Physics.

These observations link to Newton's first law, where objects maintain speed without net force, but gravity or friction alters it. Students identify examples like vehicles accelerating on roads or skaters slowing to stops. Recording qualitative changes prepares them for graphs and equations in advanced study.

Active learning benefits this topic greatly. Hands-on ramps with varied angles let students predict, test, and measure speed changes directly. Pairing predictions with timed runs fosters discussion and refines mental models, making abstract forces concrete and memorable.

Key Questions

1. Describe what happens to the speed of a ball rolling down a hill.
2. Give examples of things that get faster and things that get slower.
3. How can you make a toy car go faster or slower?

Learning Objectives

• Identify everyday objects that are speeding up or slowing down.
• Describe the qualitative change in speed for an object rolling down an incline.
• Explain how unbalanced forces cause changes in an object's speed.
• Compare the effect of different surfaces on the rate at which a toy car slows down.

Before You Start

Describing Motion

Why: Students need to be able to describe how objects move before they can describe changes in their speed.

Introduction to Forces

Why: Understanding that forces cause changes in motion is fundamental to explaining why objects speed up or slow down.

Key Vocabulary

Speed	The rate at which an object covers distance. It tells us how fast something is moving.
Acceleration	The rate at which an object's speed increases. This happens when an object speeds up.
Deceleration	The rate at which an object's speed decreases. This happens when an object slows down.
Force	A push or a pull that can cause an object to change its motion, including its speed.

Watch Out for These Misconceptions

Common Misconception

Objects slow down on their own without any force.

What to Teach Instead

Inertia keeps objects at constant speed or rest until a force acts. Ramp activities with smooth vs. rough surfaces show friction as the cause, helping students test and revise ideas through group trials.

Common Misconception

Speeding up always needs a continuous push.

What to Teach Instead

Gravity provides acceleration down inclines without pushing. Toy car ramps demonstrate this; peer predictions and timings reveal unbalanced forces, building accurate models via active experimentation.

Common Misconception

All slowing is from air resistance only.

What to Teach Instead

Friction dominates on surfaces. Station rotations with varied materials clarify multiple forces; discussions connect observations to real slowing, like brakes on cars.

Active Learning Ideas

Ramp Challenges: Speed Variations

Build ramps from books at three angles. Release identical balls or cars from the top, observe and time speed changes. Switch to rough surfaces for slowing effects, then discuss forces involved.

45 min·Small Groups

Toy Car Tracks: Acceleration Stations

Set stations with straight tracks, inclines, and curves. Students push cars gently, note speeding up or slowing, and record descriptions. Groups compare results and vote on best examples.

35 min·Pairs

Outdoor Motion Hunt: Real-World Observations

Students walk school grounds noting speeding up (e.g., downhill runs) and slowing (e.g., against wind). Sketch paths, describe changes, and share photos in class debrief.

30 min·Small Groups

Video Slow-Motion Analysis: Braking Bikes

Show bike braking videos in slow motion. Pause to predict speed changes, then measure frame-by-frame. Students draw force diagrams based on visuals.

40 min·Whole Class

Real-World Connections

• Race car engineers analyze how friction from the track and air resistance affect a car's acceleration and deceleration to optimize performance and safety during a race.
• Pilots adjust engine thrust and braking systems to control the speed of an aircraft during takeoff, landing, and flight, managing acceleration and deceleration precisely.
• Cyclists use gear changes and braking to control their speed on varied terrain, speeding up on flats and slowing down for descents or turns.

Assessment Ideas

Exit Ticket

Provide students with three scenarios: a car starting from a stoplight, a ball rolling to a stop, and a bicycle moving at a constant speed. Ask them to write 'speeding up', 'slowing down', or 'constant speed' for each scenario and briefly explain why.

Quick Check

Ask students to stand up and demonstrate 'speeding up' with their hands and 'slowing down' with their hands. Then, call out an object (e.g., 'a dropped apple', 'a skateboarder braking') and have them show the correct motion.

Discussion Prompt

Pose the question: 'Imagine you are pushing a shopping cart. What would make it speed up? What would make it slow down? What would make it stop completely?' Facilitate a class discussion, guiding students to use terms like force, friction, and pushing.

Frequently Asked Questions

How do you teach changes in speed in Senior Cycle Physics?

Start with everyday examples like balls on hills or braking cars. Use ramps for direct observation of acceleration and deceleration. Guide students to describe forces qualitatively before quantitative work. This scaffolds from observation to Newton's laws effectively.

What activities show objects getting faster or slower?

Ramp races with toy cars at different angles demonstrate speeding up from gravity. Braking stations with sandpaper tracks highlight friction's role in slowing. Outdoor hunts link to real contexts. Each builds evidence-based descriptions through hands-on trials.

How can active learning help students grasp changes in speed?

Active methods like ramp experiments let students manipulate inclines and surfaces to see speed changes firsthand. Timing runs in pairs encourages predictions and data sharing, revealing force patterns. This direct experience corrects misconceptions and strengthens connections to mechanics principles over rote learning.

What are common examples of speeding up and slowing down?

Speeding up: ball down a hill (gravity), car accelerating (engine force). Slowing down: bike braking (friction), skier on flat snow (air resistance). Class demos with everyday objects make these relatable, paving the way for force analysis in the curriculum.