force. objective use the equation: net force = mass x acceleration
TRANSCRIPT
Force
Objective
Use the equation:
net force = mass x acceleration
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sics Types of force
Gravitational force between two objects with mass
Magnetic force between two magnetic objects
Electrical force between charged objects
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sics Force, mass and acceleration
F = ma applet
Newton established that: acceleration produced by a force depends on
the mass of the object Also that if an object has no resultant force on
it, it will not accelerate eg a car travelling at a constant velocity
(balanced force) has no resultant force, and therefore no acceleration
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sics Force, mass and acceleration
A resultant force always causes acceleration
Zero resultant force implies constant velocity (which may be zero)
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sics Force, mass and acceleration
Newton established that: acceleration is proportional to force acceleration is inversely proportional to mass, if
the force is constant
Newton’s Second Law:
“The acceleration produced by a force when it acts on a body is proportional to the force and takes place in the direction of the force”
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sics Force, mass and acceleration
F = ma
where F = force in Newtons (N)
m = mass in kilograms (kg)
a = acceleration (ms-2)
Objective
F = ma practical
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accelerating washers
washers
trolley
mask size 1 cm
light gates
(resourcefulphysics.org)
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Plot a graph of acceleration (y – axis) against force (x- axis).
Use the graph to answer the following questions:
1 From Newton’s 2nd Law you would expect the graph of acceleration against force to be a straight line which passes through the origin.
2 Explain why you would expect this to be the case.
3 Explain what the gradient of the graph represents.
4 Calculate the gradient of the graph and explain whether it agrees with your answer to question (3).
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5 Your results may show some scatter. Explain why this might be and the causes of any inaccuracy.
6 Does the experimental result support Newton’s Second Law of Motion?
Objective
Define the Newton
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One Newton is the force that will give a mass of one kilogram an acceleration of one metre per second squared
1 N = 1 kg x 1 ms-2
Objective
Explain why F = ma cannot be used for a particle travelling at very high speeds
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Explain why F = ma cannot be used for a particle travelling at very high speeds
According to Einstein’s Theory of Special Relativity, at speeds approaching the speed of light, the mass of a body increases
This means that at very high speeds, Newton’s 2nd Law is invalid
This is unlikely to affect the majority of calculations!
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A car of mass 500kg is travelling at 20 ms-1. The driver sees a red traffic light ahead, and slows to a halt in 10 s. What force must the brakes provide to do this?
a = v – u / t
= 0 ms-1 – 20 ms-1 / 10 s
= 2 ms-2
F = ma
= 500 kg x 2 ms-2
= 1000 N
Questions
Physics 1
Page 29
SAQ’s 1 - 4