Chapter 4 – Explaining Motion

"What does Newton's Third Law state?"

"Whenever two objects interact, the forces they exert on each other are equal and opposite."

"Give an example of Newton's Third Law (rocket)."

"Rocket exerts a force on gases being ejected; gases exert equal and opposite force on the rocket, lifting it off."

"Give an example of Newton's Third Law (book on table)."

"The weight of the book (Earth pulling on it) = the pull of the book on the Earth."

"What is a force?"

"A push or pull that acts on an object due to interaction with another object."

"What are the two main types of forces?"

"Non-contact forces and contact forces."

"Give examples of non-contact forces."

"Electrostatic (charges attract/repel), Gravitational attraction (masses attract)."

"Give examples of contact forces."

"Normal contact force, Friction (caused by rough surfaces in contact)."

"What is a vector?"

"A quantity with magnitude and direction."

"What is a scalar?"

"A quantity with magnitude only (no direction)."

"Can vectors be negative?"

"Yes, because they have direction."

"Can scalars be negative?"

"Generally no, scalars cannot be negative."

"Give examples of scalar quantities."

"Speed, Distance, Mass, Time, Energy."

"Give examples of vector quantities."

"Velocity, Displacement, Weight, Acceleration, Force."

"Displacement cliff example."

"Above cliff = positive displacement, below cliff = negative displacement."

"How can vectors be represented?"

"By arrows: length = magnitude, direction = vector direction."

"What is the equation for weight?"

"W = m × g"

"What does W=mg represent?"

"Weight = mass × gravitational field strength."

"What is the value of g on Earth?"

"10 N/kg."

"How can weight be measured?"

"Using a force meter (spring balance) or a weighing scale."

"What happens to mass and weight on different planets?"

"Mass stays the same, but weight changes because g is different."

"What is the acceleration of free fall on Earth?"

"10 m/s² (equal to g)."

"Where does an object's weight act?"

"Through its centre of mass."

"What is distance?"

"How far an object moves, scalar quantity."

"What is displacement?"

"Distance in a straight line from start to finish with direction, vector quantity."

"What is speed?"

"Distance per unit time, scalar quantity."

"What is velocity?"

"Speed in a given direction, vector quantity."

"Typical walking speed?"

"1.5 m/s."

"Typical running speed?"

"3 m/s."

"Typical cycling speed?"

"6 m/s."

"Typical wind speed?"

"5-7 m/s."

"Speed of sound in air?"

"330 m/s."

"What is the formula for speed?"

"Speed = Distance ÷ Time."

"How do you calculate average speed for non-uniform motion?"

"Total distance ÷ total time."

"What is the formula for acceleration?"

"a = Δv ÷ t"

"What is the SUVAT equation?"

"v² = u² + 2as"

"What does the gradient of a displacement-time graph show?"

"Velocity."

"What does a horizontal line mean on a displacement-time graph?"

"Stationary object."

"What does a negative gradient mean on a displacement-time graph?"

"Returning to starting point."

"What does the area under a velocity-time graph represent?"

"Distance travelled."

"What does the gradient of a velocity-time graph show?"

"Acceleration."

"What does a horizontal line mean on a velocity-time graph?"

"Constant speed."

"What does a negative gradient mean on a velocity-time graph?"

"Deceleration."

"What does Newton's First Law state?"

"An object has constant velocity unless acted on by a resultant force."

"What happens if no resultant force acts on a stationary object?"

"It will remain stationary."

"What happens if no resultant force acts on a moving object?"

"It will continue moving at the same velocity."

"What is a resultant force?"

"A single force representing the sum of all forces acting on an object."

"Skydiver example - initial fall."

"Only force is weight, resultant force = weight, so accelerates."

"Skydiver example - increasing speed."

"Air resistance increases, resultant force decreases, acceleration slows."

"Skydiver example - terminal velocity."

"Air resistance = weight, resultant force = 0, moves at constant velocity."

"What is momentum?"

"Momentum = mass × velocity (p = mv)."

"What is the unit of momentum?"

"kg m/s."

"Is momentum scalar or vector?"

"Vector (depends on direction)."

"What does conservation of momentum mean?"

"Total momentum before = total momentum after (if no external forces)."

"What is Newton's Second Law (simple form)?"

"F = ma."

"What does inertia mean?"

"The tendency of objects to stay at rest or in uniform motion."

"What is inertial mass?"

"Force ÷ acceleration."

"What is Newton's Second Law in terms of momentum?"

"Force = rate of change of momentum."

"What is the equation linking momentum change and force?"

"Δp = F × t."

"What happens to velocity in circular motion?"

"Direction constantly changes, so velocity changes."

"Why is circular motion acceleration?"

"Velocity is changing direction, so there is acceleration."

"What is a moment of a force?"

"Moment = Force × perpendicular distance from pivot."

"What are the conditions for equilibrium?"

"Sum of clockwise moments = sum of anticlockwise moments."

"What do levers and gears do?"

"Transmit rotational forces and act as force multipliers."

"What is stopping distance?"

"Thinking distance + braking distance."

"What affects thinking distance?"

"Speed, reaction time, tiredness, drugs/alcohol, distractions."

"What affects braking distance?"

"Speed, road condition, tyres, brakes, vehicle weight."

"What is a typical human reaction time?"

"0.2-0.9 seconds."

"How is reaction time measured experimentally?"

"Using the ruler drop test."

"What happens when brakes are applied?"

"Work done by friction reduces kinetic energy, brakes heat up."

"Why is greater speed dangerous for braking?"

"More kinetic energy, requires more force, can cause overheating and loss of control."

"How do seatbelts reduce injury?"

"Stretch to increase impact time, reduce force on passengers."

"How do crumple zones work?"

"Deform to absorb energy, increase impact time, reduce force."

"How do airbags work?"

"Inflate to cushion head, increase impact time, reduce force on neck/head."

"What is kinetic energy formula?"

"Ek = ½mv²."

"What is gravitational potential energy formula?"

"Ep = mgh."

"What is the equation for work done?"

"Work = Force × Distance."

"What is 1 joule?"

"Work done when 1 N force moves an object 1 m."

"What is power?"

"Rate of energy transfer or work done."

"What is the formula for power?"

"P = E ÷ t or P = W ÷ t."