Edexcel GCSE 9-1 Physics - SP1 + SP2: Motion and Forces

Paper 1 Specification: https://qualifications.pearson.com/content/dam/pdf/GCSE/Science/2016/Specification/GCSE_Physics_Spec.pdf

What is a scalar quantity?

a quantity that has magnitude (size) but no specific direction

• e.g. speed, mass, distance

What is a vector quantity?

a quantity that has BOTH magnitude (size) and a specific direction

• e.g. acceleration, displacement, force, momentum, velocity, weight

What is velocity?

velocity is speed in a stated direction

What is the formula for speed?

speed (m/s) = distance (m) / time (s)

What is the formula for acceleration?

acceleration (m/s²)= (change in velocity) (m/s) / time taken (s)

What is the formula for the change in velocity²?

v²-u² (m/s) = 2*a(m/s²) *d (m)

What is the formula for finding the gradient of an upwards slope on a velocity time graph?

acceleration (m/s²)= (change in velocity) (m/s) / time taken (s)

What are light gates and how are they used to determine speeds of objects?

• a light gate can be used to start a timer when an object passes through it

• a flag on top of the moving object blocks a beam of light as it passes through the light gate, triggering the timer to start

• a second light gate (at some fixed distance away) can be used to stop the timer as the object passes through it

  • s = d / t

Recall some typical speeds encountered in everyday experience for wind and sound, and for walking, running, cycling and other transportation systems

• wind = 5-20 m/s

• walking = 1.4 m/s

• running =8.7 m/s

• cycling = 5-12 m/s

• cars in town = 13 m/s

• cars on a motorway = 31 m/s

• trains = <5.5 m/s

Recall Newton’s first law

• where the resultant force on a body is zero, i.e. the body is moving at a constant velocity or is at rest

• where the resultant force is not zero, i.e. the speed and/or direction of the body change(s)

Recall Newton’s second law

force (N) = mass (kg) * acceleration (m/s²)

OR

force (N) = change in momentum (N/kg) => (mv-mu)/t (s)

What is the formula for weight?

weight (N) = mass (kg) * gravitational field strength (N/kg)

Core Practical: Investigate the relationship between force, mass and acceleration by varying the masses added to trolleys

acceleration is a change in speed over time, so find the difference in the two speeds and divide by the time taken to move between the two light gates

What does an object moving in a circular orbit have?

an object moving in a circular orbit at constant speed has a changing velocity

What else is there to aid circular motion?

for motion in a circle there must be a resultant force known as a centripetal force that acts towards the centre of the circle

What is inertial mass?

inertial mass is a measure of how difficult it is to change the velocity of an object (including from rest) and know that it is defined as the ratio of force over acceleration

Recall Newton’s third law

whenever two objects interact, they exert equal and opposite forces on each other

• e.g. car tire on a road

  • the tire pushes the road backward

  • the road exerts an equal force forward on the tire

Define momentum and state its formula

• the product of an object’s mass and velocity

• a vector quantity, meaning it has both magnitude and direction.

• concept that describes the force or speed of an object in motion

  • p (kg m/s) = m (kg) * v (m/s)

Describe examples of momentum in collisions

a heavier object moving quickly will have greater momentum than a lighter object with the same velocity

• e.g. a pool table - the total momentum before the collision (solely possessed by the first ball) equals the total momentum after the collision (shared by both balls)

Explain methods of measuring human reaction times and recall typical results

Aim: Determine whether factors like caffeine or background noise affect reaction times.

• Person A holds out their hand with a gap between their thumb and first finger.

• Person B holds a ruler with the zero mark at the top of Person A’s thumb.

• Without warning, Person B drops the ruler, and Person A must catch it.

• Record the measurement on the ruler level with the top of Person A’s thumb.

• Repeat the ruler drop test several times to calculate the mean average distance caught. This distance can be equated to a reaction time.

  • The further down the ruler the catch occurs, the slower the reaction time.

  • Noise and other factors can influence reaction times

What is stopping distance the sum of?

stopping distance = braking distance + thinking distance

How is the stopping distance of a vehicle affected by the mass of the vehicle?

the higher the mass, the more friction is needed to stop the subject- braking friction must work over a greater distance to remove the larger kinetic energy

How is the stopping distance of a vehicle affected by the speed of the vehicle?

• the thinking distance is the time it takes for a driver to react to a hazard and apply the brakes

• at higher speeds, the car covers a greater distance while the driver realizes the need to brake

• small increases in speed result in bigger increases in stopping distances

How is the stopping distance of a vehicle affected by the driver’s reaction time?

• at higher speeds, the car covers a greater distance while the driver realises the need to brake

• a longer reaction time directly increases the total stopping distance

• if a driver takes longer to react to a hazard (due to distractions, fatigue, or other factors), the car will continue moving during that delay

How is the stopping distance of a vehicle affected by the state of the vehicle’s brakes?

• braking distances increase significantly with speed

• larger and heavier vehicles have longer braking distances

• wet or icy road conditions can increase braking distance

  • even small increases in speed result in significantly longer braking distances

How is the stopping distance of a vehicle affected by the state of the road?

• wet or icy road conditions can increase braking distance as there is less friction for the vehicle to stop and therefore reduce the grip/traction of tires on the road surface

  • if breaking distance increases, so does stopping distance

How is the stopping distance of a vehicle affected by the amount of friction with tyres and the road surface?

• tire tread designs are carefully engineered to provide good traction in various conditions

• on wet roads, tread patterns channel water away from the tire’s contact surface to prevent hydroplaning (when a layer of water acts as a lubricant, causing the car to “ski” on the road)

• dry roads allow for higher coefficients of friction (around 0.7), while wet roads reduce the coefficient to about 0.4 due to reduced tire-road grip

Describe the factors affecting a driver’s reaction time including drugs and distractions

• driving under the influence of drugs significantly increases reaction time as it impairs concentration, judgement and motor skills

• distracted drivers react more slowly to sudden events on the road as they divert attention

Explain the dangers caused by large decelerations and estimate the forces involved in typical situations on a public road

the higher the mass, the lower the acceleration

large decelerations:

• loss of control

• brake overheating

• potential injuries and discomfort

Carry out calculations on work done to show the dependence of braking distance for a vehicle on initial velocity squared

work done to stop a vehicle = initial kinetic energy (1/2 mv²)