# IGCSE Physics Section 1/A

What is the formula for average speed?
Average speed= distance/time taken
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What is acceleration? And what are its units?
How quickly the velocity is changing. m/s squared
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What is the formula for acceleration?
acceleration= change in velocity/time taken. a= v-u/t
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On distance/displacement- time graphs, what do certain features that could occur show?
gradient of line shows speed, flat sections where gradient is 0, the object has stopped. When the line moves towards x-axis, the object is travelling back to starting position.Straight line=constant speed. Curved line= acceleration or deceleration.
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How would you work out speed on a d-t graph?
Work out the gradient by doing rise/run USING THE CORRECT SCALE.
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On velocity- time graphs, what do certain features that could occur show?
The gradient shows acceleration. Flat sections show that the velocity is not changing so it is going at a constant speed. Steeper graph shows greater acceleration. Area under=distance traveled. A curve means change in acceleration.
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What is gravity and weight?
Gravity is the force of attraction between all masses. On the surface of a plant, gravity makes all objects accelerate towards the ground. It gives everything a weight. It keeps planets in orbit. Weight is caused by the pull of gravity.
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What is mass?
Mass is the amount of 'stuff' or matter there is in an object. This has the same value anywhere in the universe, because the amount of matter does not change. IS NOT A FORCE, it is measured in kg or g.
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What is the formula to calculate weight?
Weight = mass x gravitational field strength.
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In what three ways can friction occur?
) Friction between two solid surfaces which are gripping together (static friction.) 2) Friction between solid surfaces which slide past eachother. 3)Resistance from fluids such as liquids and gases.
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What is free-fall?
When an object is falling with no driving force apart from gravity. A free falling object through a fluid will eventually reach terminal velocity.
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Why does terminal velocity happen?
When the free fall begins, the object is accelerating, with less resistance or friction to impeed it. As the speed increases, the resistance builds, until it is equal to the driving force. The object will continue at a constant speed.
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What is an experiment to test terminal velocity?
An experiment to show terminal velocity would be to collect sycamore seeds with similar masses, but varying wing lengths, then drop them from the same height and time how long they take to reach the ground.
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If the forces on an object are balanced, what two things can happen?
If it is already moving, it will continue at a constant speed. If it is not moving, it will remain stationary.
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What does a resultant force always lead to?
A acceleration or deceleration of some type, which can include speeding up, slowing down, starting, stopping or changing direction.
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Force = mass x ?
acceleration
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In F=ma, what is F?
F is always the resultant force.
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Describe Newton's third law
IF OBJECT A EXERTS A FORCE ON OBJECT B, THEN OBJECT B EXERTS AN EQUAL FORCE ON OBJECT A. if you push an object, for example a child's pram, the object pushes back with exactly the same force (opposite.)
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Taking Newton's third law into consideratoin, why do things move?
they do not necessarily stay still, because the two objects have different masses, so therefore they accelerate at different rates away from eachother.
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What is resultant force?
The resultant force is the size of all the different forces acting on an object and their direction.
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What is stopping distance?
Stopping distance is the time is takes between when the driver first notices the hazard or problem, to when the car is completely stationary.
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How do you work out the stopping distance?
Stopping distance= Thinking distance+ braking distance
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What factors affect the thinking distance?
How fast you are going, because whatever your reaction time, the further you will travel anyway. The driver's alertnes, as influences slow reaction times, making distances longer.
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What factors affect the breaking distance?
The speed of the vehicle and its mass as it has a higher momentum (harder to stop.) The quality of the brakes, the tyre quality and weather and road surface, as this affects the grip.
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What is the equation for momentum?
Momentum (kg m/s)= Mass (kg) x Velocity (m/s)
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Explain what is meant by 'Momentum Before= Momentum After'
Momentum is conserved when no external forces act. The total momentum after is the same as it was before.When force acts on an object, it causes a change in momentum.
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State the formula linking force, the change in momentum, and the time taken.
Force acting (N)= Change in momentum (kg m/s)/ time taken for change to happen (s)
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How to seat belts, airbags and crumple zones work, in relation to momentum?
Air bags, seat belts in cars slow you down more gradually, and crumple zones crumple on impact to produce less force. (change in momentum over a larger time, aka divided by a larger number gives you a smaller result.)
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What is a moment? and hoiw do you work out the value of a moment?
Moment (Nm) = Force (N) x Perpendicular distance (m) between the line of action and pivot
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How do you get a maximum moment?
Push at a right angle to the object
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Where is the centre of gravity of an object?
The centre of gravity is directly below the point of suspension
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WHEN AN OBJECT IS BALANCED, TOTAL ANTICLOCKWISE MOMENTS= ?
WHEN AN OBJECT IS BALANCED, TOTAL ANTICLOCKWISE MOMENTS= TOTAL CLOCKWISE MOMENTS.
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If a light rod is supported at both ends, will the support be the same at both ends, if not, which will provide a larger support?
If an object is placed on the light rod, the support which is closer to the object will provide a larger force.
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What does Hooke's Law state?
That extension is proportional to force.
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What will happen to an object, when it is stretched past its elastic limit?
If a material returns to its original shape once the forces are removed, it shows elastic behaviour. Beyond the elastic limit, the material shows a plastic behaviour, where it will deform and never retain its original shape.
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What do the different sections of the Hooke's Law graph show?
The first linear section shows where Hooke's Law is being obeyed, and the extension is proportional to the force applied. However, when it curves, or suddenly changes, it highlights the objects elastic limit being exceeded.
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What is a galaxy?
A galaxy is a large collection of billions of stars
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What is the universe?
A large collection of billions of galaxies.
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Where is our solar system?
In the Milky Way galaxy
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What is an orbit?
the balance between forward motion of the object, and the force pulling it inwards.
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What processes does gravity cause?
The moon to orbit the earth, and other moons to orbit other planets. Artificial satellites to orbit the earth, and comets which are lumps of icy rock to orbit the sun.
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Why do planets nearer to the sun have a quicker orbit/move faster?
Gravity increases when objects are closer to eachother.
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What shape is the orbit of a comet, and why?
It is very elliptical, as comets travel to and from the outer edges of solar systems. When they are nearer to the sun, they travel more quickly, due to gravity.
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What is the formula for the speed of an orbit?
orbital speed= 2 x π x orbital radius / time period. Because 2πr is the circumference of a circle.
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## Other cards in this set

### Card 2

#### Front

What is acceleration? And what are its units?

#### Back

How quickly the velocity is changing. m/s squared

### Card 3

#### Front

What is the formula for acceleration?

### Card 4

#### Front

On distance/displacement- time graphs, what do certain features that could occur show?

### Card 5

#### Front

How would you work out speed on a d-t graph?