5.6.5 Estimating Decelerating Forces

Deceleration

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Deceleration is a reduction in speed or negative acceleration. When a car slows down, a decelerating force is applied. This is often caused by friction or air resistance.

The magnitude of the decelerating force can be estimated using the following formula:

F = \frac{{m \cdot \Delta v}}{{\Delta t}}

where:

F is the decelerating force (in Newtons),
m is the mass of the object (in kilograms),
Δv is the change in velocity (in meters per second),
Δt is the time over which the deceleration happens (in seconds).

Factors Influencing Deceleration

Mass of the vehicle: Heavier vehicles require more force to decelerate over the same time period.
Speed of the vehicle: The faster the vehicle is moving, the greater the decelerating force required to stop it in a given time.
Road conditions: Slippery surfaces, such as ice, reduce the available friction, making it harder to decelerate.

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Example: Estimating Decelerating Force

Imagine a car of mass 1,200 kg travelling at 30 m/s comes to a stop in 5 seconds. The decelerating force can be calculated as:

F = \frac{{1,200 \times 30}}{{5}} = 7,200 \, \text{N}

Thus, a force of 7,200 N is required to bring the car to a stop in 5 seconds.

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Key Points

The decelerating force depends on both the mass of the vehicle and how quickly it needs to stop.
Braking distance and stopping time increase with speed due to the greater decelerating forces required.
Friction between the tyres and the road surface plays a crucial role in generating the necessary decelerating force.

Estimating Decelerating Forces Simplified Revision Notes for GCSE AQA Physics Combined Science

5.6.5 Estimating Decelerating Forces

Deceleration

Factors Influencing Deceleration

Example: Estimating Decelerating Force

Key Points

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