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  • Created on: 01-01-11 16:11
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Forces and Motion:
Representing motion:
The slope on a distancetime graph represents the speed of an object. The velocity of an object
is its speed in a particular direction. The slope on a velocitytime graph represents the
acceleration of an object. The distance travelled is equal to the area under a velocitytime graph.
Speed, distance and time:
When an object moves in a straight line at a steady speed, you can calculate its speed if you know
how far it travels and how long it takes.
For example, a car travels 300 metres in 20 seconds.
Its speed is 300 ÷ 20 = 15m/s.
Distancetime graphs:
The vertical axis (yaxis) of a distancetime graph is the distance travelled from the start. The
horizontal axis (xaxis) is the time from the start. When an object is stationary, the line on the graph
is horizontal. When an object is moving at a steady speed, the line on the graph is straight, but
sloped.
The steeper the line, the greater the speed
of the object. The blue line is steeper than
the red line because it represents an object
moving faster than the one represented by
the red line. The red lines on the graph
represent a typical journey where an object
returns to the start again. Notice that the line
representing the return journey slopes
downwards.
Velocitytime graphs:
The velocity of an object is its speed in a
particular direction. This means that two cars
travelling at the same speed, but in opposite

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The vertical axis (yaxis) of a velocitytime graph is the velocity
of the object. The horizontal axis (xaxis) is the time from the start.
When an object is moving with a constant velocity, the line on the graph is horizontal. When an
object is moving with a constant acceleration, the line on the graph is straight, but sloped.
The steeper the line, the greater the acceleration of the object.…read more

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The gradient of a line on a distancetime graph represents the speed of the object.
1) What is the speed represented by the blue line?
The object travels 10m in 2s.
Its speed is 10 ÷ 2 = 5m/s.…read more

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Velocitytime graphs:
The gradient of a line on a velocitytime graph represents the acceleration of the object.
1) What is the acceleration represented by the sloping line?
The object increases its velocity from 0m/s to 8m/s in 4s.
Its acceleration is 8 ÷ 4 = 2m/s2.…read more

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The area under the line in a velocitytime graph represents the distance travelled. To find the
distance travelled in the graph above, we need to find the area of the lightblue triangle and the
darkblue rectangle.
1) Area of lightblue triangle :
The width of the triangle is 4 seconds and the height is 8 metres per second.…read more

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Area under the whole graph
The area of the lightblue triangle plus the area of the darkblue rectangle is:
16 + 48 = 64m.
This is the total area under the distancetime graph. This area represents the distance
covered.
Forces. Masses and Acceleration:
A stationary object remains stationary if the sum of the forces acting upon it, the resultant force,
is zero. A moving object with a zero resultant force keeps moving at the same speed and in the
same direction.…read more

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Forces and acceleration:
An object will accelerate in the direction of the resultant force. The bigger the force, the greater the
acceleration. Doubling the size of the (resultant) force doubles the acceleration.
An object will accelerate in the direction of the resultant force. A force on a large mass will
accelerate it less than the same force on a smaller mass. Doubling the mass halves the
acceleration.…read more

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Put in the values.
o Acceleration = 3,000N 2,000kg
4) Work out the answer and write it down.
o Acceleration = 1.5m/s2
Here are four typical forces on which you could be asked questions:
1) Air resistance (drag): When an object moves through the air, the force of air resistance acts
in the opposite direction to the motion. Air resistance depends on the shape of the object and its
speed.
2) Contact force: This happens when two objects are pushed together.…read more

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Also, there is friction between the road and the tyres. There is friction in the wheel
bearings. And air resistance acts on the front of the car.
Weight and friction:
Gravity is a force that attracts objects with a mass towards each other. The weight of an object is
the force acting on it due to gravity. The gravitational field strength of the Earth is 10 N/kg. The
stopping distance of a car depends on two things: the thinking distance and the braking distance.…read more

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Falling objects:
You should be able to describe the forces affecting a falling object at different stages of its fall.
Usually, you need to think about two forces:
1) The weight of the object This is a force acting downwards caused by the object's mass and
the Earth's gravitational field.
2) Air resistance This is a frictional force acting in the opposite direction to the movement of the
object.…read more

Comments

rgs.himanshu

Well developed and concise. Useful for students for revision before they begin Past paper Solving

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