AQA · GCSE · Physics

    Course version: 8463 · Version from Sept 2016

    So, when a vehicle travels at a steady speed the resistive forces balance…

    Full specification wording

    Newton's First Law: So, when a vehicle travels at a steady speed the resistive forces balance the driving force.

    A vehicle is pushed forward by a driving force from the wheels and held back by resistive forces, mainly air resistance plus friction.

    Checked against the AQA 8463 specification (opens in a new tab) on .

    • Point 2 of 5
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    A vehicle is pushed forward by a driving force from the wheels and held back by resistive forces, mainly air resistance plus friction. Air resistance grows as the vehicle goes faster, because the car sweeps through more air every second. When a driver accelerates, the driving force is larger than the resistive forces, so there is a resultant forward force. As the speed rises the resistive forces catch up, the resultant force shrinks and the acceleration falls. At maximum speed the resistive forces have grown until they equal the driving force, the resultant force is zero and the speed stays constant. The driving force has not fallen; the drag has risen to meet it. A steeper hill or a headwind raises the resistive forces at every speed, so the same engine reaches a lower maximum speed.

    What earns the marks

    • The driving force being greater than the resistive forces, giving a resultant forward force.
    • Air resistance increasing as the speed of the vehicle increases.
    • The resultant force decreasing, so the acceleration decreases.
    • Air resistance becoming equal to the driving force at maximum speed, so the resultant force is zero.

    Common mistakes and how to put them right

    • Saying the driving force decreases as the car speeds up, when it is the air resistance that increases.

    • Claiming air resistance becomes greater than the driving force at top speed, which would make the car slow down.

    • Describing only the forces at maximum speed and ignoring how they changed on the way there.

    • Using the vague word friction for a car moving through air rather than air resistance or drag.

    Exam tips

    • In a levels-marked 'explain how the forces change' question, track both forces from the start of the acceleration to maximum speed.
    • Finish with the sentence 'the resultant force is now zero', which is usually needed for the top level.
    • Label arrow lengths on a force diagram to show which force is larger at each stage.

    Try the lesson

    The start of the Newton's First Law: So, when a vehicle travels at a steady speed the resistive forces balance the driving force. lesson, made from checked teaching notes for this specification point.

    Have a go first

    A car is travelling along a straight, level road at a steady speed. Which statement describes the driving force and the resistive forces acting on the car?

    Listen

    A vehicle is pushed forward by a driving force from the wheels and held back by resistive forces, mainly air resistance plus friction. Air resistance grows as the vehicle goes faster, because the car sweeps through more air every second. When a driver accelerates, the driving force is larger than the resistive forces, so there is a resultant forward force. As the speed rises the resistive forces catch up, the resultant force shrinks and the acceleration falls. At maximum speed the resistive forces have grown until they equal the driving force, the resultant force is zero and the speed stays constant. The driving force has not fallen; the drag has risen to meet it. A steeper hill or a headwind raises the resistive forces at every speed, so the same engine reaches a lower maximum speed. A strong answer earns marks for these points. the driving force being greater than the resistive forces, giving a resultant forward force. air resistance increasing as the speed of the vehicle increases. the resultant force decreasing, so the acceleration decreases. air resistance becoming equal to the driving force at maximum speed, so the resultant force is zero. Exam tip: In a levels-marked 'explain how the forces change' question, track both forces from the start of the acceleration to maximum speed.

    See it

    A top-to-bottom flowchart with nine boxes joined by arrows. The first box says the driver accelerates with driving force larger than resistive forces, leading to a resultant forward force. That leads to speed rising, which leads to air resistance increasing as speed increases. Air resistance increasing leads to the resistive forces catching up, which leads to the resultant force shrinking, which leads to acceleration falling. Acceleration falling leads to maximum speed, where air resistance equals the driving force, and finally to the resultant force being zero and the speed staying constant.
    It shows how, as a vehicle speeds up, air resistance rises until it equals the driving force, the resultant force falls to zero and the speed becomes constant.

    Key words

    Say what each word means before you turn the card.

    driving force

    Try answering aloud or in your head before turning the card.

    air resistance

    Try answering aloud or in your head before turning the card.

    resultant force

    Try answering aloud or in your head before turning the card.

    maximum speed

    Try answering aloud or in your head before turning the card.

    See every definition
    driving force
    The force from the wheels that pushes a vehicle forward.
    air resistance
    A resistive force that grows as the vehicle goes faster, because the car sweeps through more air every second.
    resultant force
    The overall force left when the resistive forces are taken from the driving force; it is zero at maximum speed.
    maximum speed
    The speed at which the resistive forces have grown until they equal the driving force, so the speed stays constant.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-to-bottom flowchart with nine boxes joined by arrows. The first box says the driver accelerates with driving force larger than resistive forces, leading to a resultant forward force. That leads to speed rising, which leads to air resistance increasing as speed increases. Air resistance increasing leads to the resistive forces catching up, which leads to the resultant force shrinking, which leads to acceleration falling. Acceleration falling leads to maximum speed, where air resistance equals the driving force, and finally to the resultant force being zero and the speed staying constant.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

    There is more to this lesson

    The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.

    Carry on with the full lesson

    A week of Premium from your first lesson · Then the free plan continues · No card, no charge

    Test your understanding of Newton's First Law: So, when a vehicle travels at a steady speed the resistive forces balance the driving force.

    Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.

    Take topic quiz

    A week of Premium from your first lesson · Then the free plan continues · No card, no charge

    Start free

    Cookies on MasteryMind

    Essential cookies keep you signed in.

    Analytics and advertising cookies stay off unless you accept.

    Read our Privacy Policy.