Forces (P5) Flashcards
What are vector quantities?
A quantity with both magnitude and direction
What are scalar quantities?
A quantity with magnitude but no direction
What type of quantity is Force?
Vector
What type of quantity is Velocity?
Vector
What is a force?
A push or pull on an object that is caused by interacting with something
What are the two types of forces?
Contact
Non-Contact
What is a contact force?
When the two objects must be touching for a force to act
What is a non-contact force?
When the two objects don’t need to be touching for a force to act
What type of quantity is Displacement?
Vector
What type of quantity is Speed?
Scalar
What type of quantity is Acceleration?
Vector
What type of quantity is Momentum?
Vector
What type of quantity is Distance?
Scalar
What type of quantity is Mass?
Scalar
What type of quantity is Temperature?
Scalar
What type of quantity is TIme?
Scalar
What type of force is Friction?
Contact
What type of force is Normal Contact Force?
Contact
What type of force is Electrostatic Force?
Non-Contact
What type of force is Gravitational Force?
Non-Contact
What is gravitational force?
The force of attraction between masses
What are the two most important effects of gravity?
Makes all things on the surface of a planet fall to the ground
Gives everything weight
Define Mass
How much matter and object contains (kg)
What is the mass of a box that has a mass of 500kg on Earth, in space?
500kg
Is the weight of an object on Earth equal to its mass?
No, as it experiences gravity
What is the Earth’s Gravitational Field Strength (g)?
9.8N/kg of mass
What is weight measured in?
Newtons (N)
Give the equation for Weight
Weight = mass x gravitational field strength
What is the relationship between weight and mass?
Weight ∝ Mass
What do we use to calculate weight?
Calibrated Spring Balance or Newtonmetre
Define Centre of Mass
Where the weight of an object can be considered to act (due to gravity)
Describe Resultant Force
A single force that has the same effect as all the original forces acting together
What does it mean if the resultant force is 0N?
The object is moving at a constant pace or is stationary
How is an object shown in a free body diagram?
A point
How is force shown in a free body diagram?
Arrows from the point
What does the size of an arrow show?
Size of the force
What does the direction of the arrowhead show?
Direction of the force
Describe a vector diagram?
Draw a free body diagram to scale and then mirror it to produce a parallelogram
Measure the distance from the object to the opposite point and calculate the resultant force using your scale
What do we use vector diagrams for?
To calculate the resultant force when the forces are not parallel
What does it mean to resolve a force?
Taking one force that is working at an angle, and splitting it into its vertical and horizontal values
How do we resolve forces?
Using a vector diagram
Describe how to resolve a force?
Draw a vector diagram to scale with faint axis
Draw a dotted line from the head of the force to either axis.
Measure the lengths and calculate using your scale
Define Work Done
The process of energy being transferred from one store to another
How is work done calculated?
Work done = Force x Distance
W(J) = F(N) s(m)
What must be true of the distance for W=Fs to be true?
The distance must be in the line of action of the force
What does it mean if 1J of work is done?
When a force of 1N moves an object by 1m
How many joules in 5Nm?
5J
What is Nm?
Newton-metres (or joules)
What does it mean to be in the line of action of a force?
The value must be measured in the same direction as the force
(For example a person walking up stairs is affected by gravity. There distance in line with the force is their distance from the ground, not the first step)
Define elastic object
An object that will return to its original length or shape if we take away forces acting on them
What do we call it when a force changes the shape or size of an elastic material?
Elastic Deformation
What is the minimum amount of forces that must be acting on an object for it to be deformed?
2
any less will simply unbalance the forces and cause it to move
How do we calculate the force needed to stretch an elastic object?
F=ke
Force (N) = Spring constant (N/m) x Extension (m)
When we do wo work on an elastic object, the work done is equal to ….
…The Elastic Potential Energy (as long as it has not undergone inelastic deformation)
What equipment do we need to investigate the elasticity of a spring?
A clamp stand Two basses Two Clamps Heavy Weight Meter Rule Spring Pointer
What do we use the heavy block for when we investigate the elasticity of a spring?
We place it at the bottom of the clamp stand to stop it falling over
What two things are true about the pointer when we investigate the elasticity of a spring?
It is attached to the bottom of the spring (Splint)
It is horizontal
What two things are true about the rule when we investigate the elasticity of a spring?
0cm is in line with the top of the spring
It is vertical
When investigating elasticity of a spring, what is the unstretched length?
The number the pointer sets to before any weight is applied
When investigating elasticity of a spring, how do we apply even forces each time?
By using 1N weights and making them hang off of the spring
We then measure the extension from the original
(More weights each time)
When investigating elasticity of a spring, how much weight should be applied at a time?
1N after each reading (probably about 4/5N in total)
When investigating elasticity of a spring, how do we calculate extension?
We subtract the unstretched spring from each of the readings
When investigating elasticity of a spring, how could we discover the weight of an unknown object?
Plot your results and draw a line of best fit
Measure the extension of the spring with the unknown object
Use the graph to now calculate the weight in N
When investigating elasticity of a spring, what is the relationship between extension, and the weight applied to a spring?
Directly Proportional, linear
When investigating elasticity of a spring, describe the graph of Extension vs Weight
Straight line going through the origin
y-axis is Extension (m)
x-axis is Weight (N)
HOWEVER, is too much weight is applied the gradient will have a sudden increase
Define Inelastic Deformation
When a string has been overstretched to the point where even if the forces are taken away the spring still shows an extension
(the spring has exceeded the limit of proportionality)
What is the name given to the point at which the graph of Extension vs Weight is no longer linear?
Limit of proportionality
How can we use an Extension vs Weight graph to calculate spring constant?
(This only works before the limit of proportionality)
Weight divided by the extension
Define Moment
Turning effect of a force
Equation for moment
M=Fd
Moment (Nm) = Force (N) x Distance (m)
Unit for Moment
Newton-metre (Nm)
When calculating the moment, in which direction is the distance?
Perpendicular from the line of action of the force to the pivot
When a pivot is balanced what two moments must be equal?
Clockwise moment and the anticlockwise moment
When do objects topple?
The centre of mass of the object always provides a force in the same direction
As an object tilts, this force will eventually lie outside the bass of the object and the object will topple
What is a lever?
Force multiplier
A lever is a simple machine made of a rigid beam and a fulcrum
What is a gear?
Force multiplier
Gears are wheels with toothed edges that rotate on an axle or shaft. The teeth of one gear fit into the teeth of another gear.
How large must the radius of a gear be to transmit double the turning force?
Twice that of the gear that transmitted its turning force to it.
If force is multiplied in a gear system how does the work done stay the same?
The smaller gear will turn more times than the larger one
If the turning force is doubled, the larger gear will turn once for every two the smaller gear does
What is pressure?
The force acting at right angles to the wall (along the normal) inside a container
What are fluids?
Gasses and liquids
Equation for Pressure
Pressure (Pa) = Force normal to a surface (N) / area of that surface (m^2)
(F=Pa)
Unit for pressure
Pascals (Pa)
Describe the density of the atmosphere in relation to the Earth?
The greatest density is near Earth
The lowest density is at the top of the atmosphere
What does it mean if the atmosphere is densest near Earth?
At the surface of the Earth thee are the greatest number of air molecules in a given volume
Why do crisp packets swell in a plane?
On Earth the pressure in and outside the crisps is the same
When flying, the air pressure is lower outside the crisps than inside
Therefore the packet has less resistance and inflates
Describe pressure in a container of fluid?
Highest pressure at the bottom of the container, decreases up the column
Equation for pressure in a column of liquid
P=hρg
Pressure (Pa) = Height (m) x Density (kgm^3) x Gravitational Field Strength (N/kg)
What is ρ?
rho
Represents density of liquid (kg/m^3)
Why does pressure change in a column of liquid?
As depth increases, there is a greater weight acting downwards
