Physics- Unit 2- Force and Acceleration

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  • Created by: FireDwarf
  • Created on: 24-03-14 19:35
Newton’s First Law of Motion;
Objects either stay at rest or in a uniform motion unless acted on by a force.
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What is an object moving at a constant velocity therefore?
Therefore, an object moving at constant velocity is either acted on by no forces or the forces acting on it are balanced (resultant force is zero)
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Newton’s Second Law of Motion;
Force= Mass x Acceleration (F=ma)
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Test for this?
Using a dynamics trolley and a motion sensor.
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How is the test completed?
The sensor sends messages to a computer to display how the velocity of the trolley changes over time. The trolley is pulled along a sloping runway (using an elastic band stretched to the same length).
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Why to the same lengh? Slope? To test?
To ensure the same force. Account for friction. Should move down the slope at constant speed after a push.
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What does the test show?
Velocity increases at a constant rate down the path with same mass and force. Force is proportional to mass x acceleration (increase in a when F and M increase)
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How can we use F=Ma to prove objects fall at same acceleration?
a = F/M. When gravity is only force acting on it, Mxg/M = a. Therefore a=g.
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What happens when an object is acted on by two unequal forces in opposite directions? (acceleration)
Accelerates in the direction of the larger force.
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Rocket problems?
We have two forces, the rocket thrust and the rockets weight. For it to fly thrust>weight. Therefore T-Weight= ma. Therefore thrust = ma + mg.
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Lift problems?
For a lift to move T-mg = ma.
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Lift moving at constant velocity?
T = mg
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Moving up and accelerating?whats its a like?
T= ma + mg (Tension will be larger then the mass x gravity) A>0
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Moving up and deaccelerating? whats its a like?
T= ma + mg (Mg is larger) A
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Moving down and accelerating?whats its a like?
T= ma + mg (Mg Larger) A
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Down and deaccelerating?whats its a like?
T= ma + mg (Mg is smaller). A>0
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Pulley Problems?
Mass that accelerates downwards = mg-t = ma and the one accelerating upwards = T-mg=ma.
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Slope? How to work out weight componant?
Weight down the slope = mgsin(angle)
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Equation for Force?
mgsin(angle)- friction force = ma.
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What is drag force dependant upon?
shape of the object, speed, viscosity of the fluid (How easilly the fluid flows past a surface).
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Describe the motion of a object falling in a fluid?
Speed of the object from rest increases as it falls so the drag force increases. Resultant force is the diffrence between the weight of the object and the drag force.
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what happens as the drag force increases?
As the drag force increases, the resultant force decreases (as the diffrence decreases) so acceleration becomes less.
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When does it reach terminal speed?
When the drag force is equal and opposite to the weight. Its acceleration is zero and its speed remains constant as it falls.
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Test to find out terminal velocity?
Object gets released with a thread attached which pulls a tape through a tickertimer, printing dots on the tape. Spaces between tapes get longer as speed increases as are taken in a constant rate. Tapes will be a constant size at terminal velocity.
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How to work out the resultant force?
F = mg -D
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How to find the acceleration therefore?
a = mg-D/m
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What happens at terminal speed (related to energy)?
Potential energy lost by the object is converted as it falls to internal energy of the fluid by the drag force.
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What is stopping distance (sum and explanation)?
Thinking distance + breaking distance. It is therfore the time for when a hazard is spotted to the time where the car reaches a full stop.
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Thinking distance?
Time taken for the driver to spot a hazard and then react. For a vehicle moving at constant velocity, it is speed x reaction time.
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effected by?
Alcohol, drugs, distractions (eg:phones).
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Breaking distance?
Distance travelled by the car from when the brakes are applied to when the car reaches a full stop.
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Equation?
v2/2a
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formula for impact force? also?
Change in kinetic energy/impact distance OR F=ma
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Name 5 car safety features?
Bumpers, crumple zones, seat belts, collapsible steering wheel, airbags
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Bumpers?
These give way a little during a collision which causes the impact time to increase at a low-speed impact. If impact time is reduced, impact force is reduced.
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Crumple zones?
Engine compartment gives way in a front-end impact. Increases the impact time which reduces the impact force.
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Seat belts?
The wearer stops more gradually then without them. This increases the impact time, decreasing impact force.
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Collapsible steering wheel?
Driver does not hit the wheel, reduces impact force.
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Airbags?
Acts as a cuhsion, which reduces impact force, and increases impact time. Force is also spread over a larger distance.
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Card 2

Front

What is an object moving at a constant velocity therefore?

Back

Therefore, an object moving at constant velocity is either acted on by no forces or the forces acting on it are balanced (resultant force is zero)

Card 3

Front

Newton’s Second Law of Motion;

Back

Preview of the front of card 3

Card 4

Front

Test for this?

Back

Preview of the front of card 4

Card 5

Front

How is the test completed?

Back

Preview of the front of card 5
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