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AS AQA PHYSICS MECHANICS
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Gravity
Terms in this set (76)
Each out of scalars or vectors have direction?
Vectors
Give an example of a scalar quantity
Mass, temperature, time, length/distance, speed, energy
Give an example of a Vector quantity
Displacement, velocity, force, acceleration, momentum
When you add two or more vectors together what do you find?
The resultant vector
In what ways can you find the resultant vector?
Scale drawings or Pythagoras and trigonometry
Explain how to set up a scale drawing to find the resultant vector
Draw each vector, to scale, tip-to-tail. Then draw the resultant vector from the tail of the first of the tip of the last and measure its length and angle.
Explain how you can find the resultant vector using Pythagoras/trigonometry
When two vectors are at right angles to each other, you can us Pythagoras/trigonometry to find the resultant vector
If a body is in equilibrium what will the forces acting on it be?
The forces must be in equilibrium
What does resolving a force mean?
Splitting the force into component form
How can you draw three coplanar forces acting on a body in equilibrium?
You can draw the forces as a triangle, forming a closed loop
If two forces are acting on an object, how do you find the resultant force?
By adding all the vectors together and creating a closed triangle (with the resultant force represented by the third side)
What does the moment of a force depend on?
1) Size of force
2) how far the force is applied from the turning point
What does the principle of moments state?
The principle of moments state that for a body to be in equilibrium, the sum of the clockwise moments about any point equals the sum of the anti-clockwise moments about the same point
Describe the forces acting on a lever
In a lever, an effort force acts against a load force by means of a rigid object rotating around a pivot
What does coplanar mean?
All in the same plane
What is a couple?
A couple is a pair of coplanar forces of equal size which acts parallel to each other, but in opposite directions
What does a couple produce?
A turning effect
Define mass
The mass of an object is the amount of 'stuff' in it
The greater the objects mass, is it's resistance to a change in velocity greater or lesser?
Greater
Define inertia
The resistance to a change in velocity
Does the mass of an object change if the strength of the gravitational field changes
No
Weight is the forced experienced by...
A mass due to gravitational field
Does the weight of an object change if the strength of the gravitational field changes
Yes
Define centre of mass
The centre of mass of an object is the point where you can consider its whole weight to act through
Where is the centre of mass in a uniform, regular solid
At its centre
How do you find the centre of mass in a regular object?
1) use symmetry
2) the centre of mass is at the centre where the lines of symmetry will cross
3) the centre of mass is halfway through the thickness of the object where the lines meet
How do you find the centre of mass in an irregular object?
1) hang the object freely from a point
2) using a plumb bop draw a vertical line downwards from the point of suspension
3) hang the object from a different point and repeat
4) the COM is where the lines cross
When will an object topple over?
If the vertical line drawn downwards from its centre of mass falls outside its base area. As a resultant moment occurs, which provides a turning effect
What conditions causes an object to be stable?
Low centre of mass
Wide base area
Define speed
How fast something is moving regardless of direction
Define displacement
How far an object has travelled from its starting point in given direction
Define velocity
The rate of change of an objects displacement (speed in a given direction)
Define acceleration
The rate of change of an objects velocity
How is acceleration displayed on a displacement-time graph
A curved line
How is velocity displayed in a displacement time graph
The gradient
How do you find the instantaneous velocity on a displacement time graph which displays the acceleration of a car
You need to draw a tangent to the curve at that point to find its gradient
How is acceleration displayed on a velocity time graph
A straight line
How is changing acceleration displayed on a velocity time graph
A curved line
How is displacement displayed on a velocity time graph
Area under the graph
What does the area under the an acceleration time graph show
The change in velocity
What piece of experiment can you use for motion experiments
An ultrasound position detector, a type of data logger that automatically records the distance of an object from the sensor several times a second
Give three advantages of using data loggers over traditional methods
1) more accurate- don't need to wait for human reaction times
2) automatic systems have a much higher sampling rate than humans
3) you can see the data displayed in real time
What is the only force acting on an object in free fall
Weight
What did Galileo set up to test his theory?
Galileo set up systematic and rigorous experiments. These experiment could be repeated and the results described mathematically and compared
Galileo believed that all objects fall at the same rate. But struggled to prove this as objects fall to quickly. How did he over come this problem?
He measured the time a ball took to roll down a smooth groove in an inclined pane. This slowed the balls fall as well as reducing the effect of air resistance
How do you find 'g' from a displacement time graph?
Finding the change in the gradient between two points on the graph
What's the method for working out projectile motion problems which start off at angle?
1) resolve the initial velocity into horizontal and vertical components
2) use the vertical components to work out how long it's in the air and/or how high it goes
3) use the horizontal component to work out how far it goes horizontally while it's in the air
What's Newton's 1st law state?
That the velocity of an object will remain constant unless a resultant force acts on it
What does Newton's second law state?
Acceleration is proportional to the force (That the more force you have acting on a certain mass the more acceleration you get and for a given force the more mass you have the less acceleration you get)
Is acceleration Independent or dependent of he mass?
Independent
What does Newton's third law state?
If an object A exerts a force on object B, then object B exerts an equal but opposite force on object A
For Newton's 3rd law what do the two forces have to be?
The forces have to be of the same type
What are the two mains types of friction
Fluid and dry friction
What does fluid/dry friction depend on?
1) thickness/viscosity of the fluid
2) it increases as speed increases
3) depends on the shape moving through it- larger area=larger resistance
4) A projectile is slowed down by air resistance
What should you remember about frictional forces
1) it always opposes motion
2) never speeds things up/start it moving
3) convert kinetic energy into heat and sound
What is the lift force
Lift is an upwards force on an object moving through a fluid
When does lift happen
Happens when the shape of an object causes the fluid flowing over it to change direction
In what direction does the lift force act compared to the direction the fluid flows in
Perpendicular
How does a car reach terminal speed
1) car accelerates from rest using a constant driving force
2) As speed increases, friction increases - reducing the restaurant force acting on the car and reducing its acceleration
3) frictional forces become equal to the driving force - now no resultant force and no acceleration so the car has a constant speed
What are two ways to increase a car maximum speed
1) increasing the driving force
2) reducing the frictional force
What does the momentum of an object depend on?
mass and velocity
the total momentum of two objects before the collision equals..
The total momentum after the collision.
What is conserved in an elastic collision
Momentum and kinetic
What is conserved in an inelastic collision
Momentum only
Newton's 2nd law of motion states that force is the rate of change in momentum...
Of an object is directly proportional to the resultant force which acts on the object
What does impulse equal
Change in momentum
How is impulse displayed on a force-time graph
The are underneath
How can the force of an impact be reduced
By increasing the time of impact
How do crumple zones work
The parts at the front and back of the car crumple up on impact. This causes the car to take longer to stop, therefore increasing the impact time and decreasing force of passengers
How do seat belts work
They stretch slightly increasing the time taken for the wearer to stop. Reduces forces acting on the chest
How do air bags work
These slow down passengers more gradually, and prevent them hitting hard surfaces inside the car
What does work mean
Means the amount of energy transferred from one form to another when a force causes a movement of some sort
How is work done displayed on a force displacement graph
Area underneath
Define power
The amount of energy transferred from one form to another per second
Define watt
Rate of energy transfer equal to 1 joule per second
What does the principle of conservation state
Energy cannot be created or destroyed. Energy can be transferred from one form to another but the total amount of energy in a closed system will not change
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