UNIT-1: Chapter-3
FORCES AND MOVEMENT
সুপ্রিয় ২০২৪ সালের ‘O’ level পরীক্ষার শিক্ষার্থী বন্ধুরা, শুভেচ্ছা নিও। আজ তোমাদের Physics Paper-1-এর ‘UNIT-1: Chapter-3, FORCES AND MOVEMENT’ থেকে বাকি Discussion নিয়ে আলোচনা করা হলো।
Factors Affecting Stopping Distances
Specification Point 1.20
• Describe the factors affecting vehicle stopping distance, including speed, mass, road condition and reaction time.
• The main factor affecting the stopping distance of a car is its speed.
• There are a number of other things, however, that can affect the stopping distance, by either increasing the thinking distance or the braking distance.
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Exam Tip
• Be careful about the language you use:
• If a question asks you to list a factor that increases the thinking distance, be specific in your answer: e.g. “Consuming alcohol” rather than “Whether or not you’re drunk” – the first makes it clear that drinking alcohol increases the distance, whilst the latter is slightly vague.
• Increasing reaction time is not the same thing as improving reaction time. If the reaction time increases then you take longer to react.
• If asked to list factors affecting stopping distances, try and stick to those given in the table, and only choose one from each cell (don’t give both alcohol and drugs as separate factors).
• Although there are other factors that affect stopping distances, they tend to be less clear cut: Do reactions times get worse with age or do they improve with experience?
STOPPING DISTANCE
The stopping distance is the sum of the thinking distance and the braking distance.
THINKING DISTANCE
When a driver suddenly sees an object blocking the way ahead. It takes time for him or her to respond to the new situation before taking any action, such as braking. This time is called reaction time and will depend on the person driving the car.
Thinking distance = speed of the car × reaction time
THE FACTORS EFFICTING THE THINKING DISTANCE
• If the driver is drug addicted then the reaction time will be more as well as thinking distance will be more.
• If the driver is in mental stress then reaction time will be more as well as thinking distance will be more.
• If the driver is in multitasking mode then reaction time will be more as well as thinking distance will be more.
BRAKING DISTANCE
The distance travel by the car while the car is decelerating to rest is called braking distance.
Braking distance = speed of the car × braking time
THE FACTORS EFFECTING THE BRAKING DISTANCE:
• Conditions of the road
• Conditions of the tyre
• Conditions of the brake systems
Weight, Mass & Gravity
Specification Point 1.18:
• Know and use the relationship between weight, mass and gravitational field strength:
weight = mass × gravitational field strength
W = m × g
• Mass (measured in kilograms, kg) is related to the amount of matter in an object.
• Weight (measured in newtons, N) is the force of gravity on a mass.
• The size of this force depends on the gravitational field strength (often called gravity, g, for short).
weight = mass × gravitational field strength
W = m × g
• You can rearrange this equation with the help of the formula triangle:
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Use the formula triangle to help you rearrange the equation
• The value of g (the gravitational field strength) varies from planet to planet.
• On Earth: g 10 N/kg
Exam Tip
• Mass is usually measured in kilograms in Physics.
• if it is given in grams, you might need to convert to kilograms by dividing the mass by 1000.
• It is easy to confuse mass and weight, so take care to use each term appropriately.
WEIGHT
The weight of an object is the force that acts on it because of gravity. The weight of an object depends on its mass and the strength of gravity. The gravitational field strength (g) is the force that acts on each kilogram of mass. We can work out the weight of an object by using this equation.
weight, W (N) = mass, m (kg) × gravitational field strength. g (N/kg)
W = m × g
Forces Acting on Falling Objects
Specification Point 1.21
• Describe the forces acting on falling objects (and explain why falling objects reach a terminal velocity)
• When a parachutist jumps out of an aeroplane, two main forces act:
• Weight (the force of gravity) •Air resistance
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Diagram showing how the changing forces on a skydiver
লেখক:
Assistant Teacher (Senior section)
O and A level Physics Teacher
Bangladesh International School and College, Dhaka.
জাহ্নবী
