Forces Flashcards
Define physical quantity
A physical quantity is a physical property of a phenomenon, body, or substance, which
can be quantified by measurement.
Quantity symbol of time
t
Quantity symbol of mass
m
Quantity symbol of force
F
Quantity symbol of weight
Fg
Quantity symbol of charge
Q
Si unit for seconds (t)
s
Si unit for kilograms (m)
kg
Si unit for newton (F)
N
Si unit for newton (Fg)
N
Si unit for coulomb (Q)
C
What two groups are classified as physical quantities
Scalar quantities
Vector quantities
Define Scalar quantity
A scalar quantity is a physical quantity that has
magnitude (size) only.
What does scalar quantity include?
Mass, electric charge, time, distance (MEDT) scales of fish
Define vector quantity
A vector quantity is a physical quantity that has
magnitude and direction.
What does vector quantity include?
Force, weight, velocity, acceleration (WAVF)
What are the two ways of describing direction?
Relative direction and compass points
What is relative direction?
up, down, left, right, forwards, backwards
What is compass points?
North, east, south, west
How is a vector shown?
arrow pointing to the right written above it
When is arrow left out of vector?
If the magnitude (size) of a vector is only needed, then the arrow is omitted (left out).
How are vectors graphically represented?
Arrow defining the direction, and the length of
the arrow defines the vector’s magnitude according to a scale.
How are two vectors equal?
Equal if they have the same magnitude and direction,
regardless of whether they have the same initial points,
Define forces
A force is a push or a pull that acts in a certain
direction.
What two things do forces have?
Magnitude (size) and direction
What can forces change?
Change a body’s state of motion in a straight line.
How can forces be measured?
spring scale/spring balance/newton meter (
What spring scales include?
Spring connected to a metal hook
When does the spring stretch (balance)?
Force is applied to hook
When does the spring stretch long?
The bigger the force applied, the longer
the spring stretches and the higher the reading.
When describing a force, which of the following 4 points must be noted?
exerting the force
experiencing the force
magnitude of the force
direction force is being exerted
What does the length of the arrow represent?
Represents the magnitude of the force
What does the arrowhead represent?
arrowhead represents the direction of the force.
How can we also describe the direction in which a force acts?
cardinal points system
What are free body diagrams are used to represent?
Free body diagrams are used to represent all of the forces acting on an object graphically.
What happens when more than one force can act on an object at a time?
Multiple arrows connected to the same dot.
If the forces are acting in the same direction, what do you do?
Draw separate arrows, connected to
the same dot
How does one represent force?
uppercase ‘F’ to show that it is a force,
subscript to show who or what is exerting the force.
What are the effects of forces?
Forces do not always have an effect, but the effects that they can have are the following.
Name the four effects of forces
Motion, distortion, direction, rotation
What is motion?
change the speed of an object.
cause a stationary object to move.
cause a moving object to stop.
What is distortion?
change the shape of an object.
Elastic objects return to their original shape - force removed.
Inelastic objects are permanently distorted.
What is direction?
A force can change the direction in which
something is moving.
What is rotation?
A force can cause an object to spin.
Define balanced and unbalanced forces
The resultant force (Fnet) is the single force which
has the same effect as the original forces acting
together.
What is another word for Fnet?
Resultant force
Fnet = 0
Balanced force
Fnet = 0 not
Unbalanced force
When does Fnet occur?
When multiple forces act on the same object
What are balanced forces?
Balanced forces have equal magnitudes but act in opposite directions.
Why is the resultant force zero (balanced)?
They cancel each other out and the overall effect is zero
When the forces are balanced, there is no change in the object’s state of motion:
A stationary object remains stationary
A moving object keeps on moving at the same speed in the same direction
What are unbalanced forces?
do not have equal magnitudes
do not cancel each other
What effects do unbalanced forces have on?
overall effect on the body
How does one show forces graphically?
Head to tail diagrams
How does one calculate forces graphically?
Algebraically
What is the formula to determine the resultant force?
Fnet = F1 + F2
What formula must one use when calculating the resultant force acting in the same direction?
Fnet = F1 + F2
What formula must one use when calculating the resultant force not acting in the same direction?
Assign one direction positive - other negative
Fnet = F1 + F2
= + + (-)
When describing resultant force, what must one include?
Magnitude and direction
What do forces occur in?
Pairs
When forces occur in pairs, what is it called?
• Act on two different objects
• Have the same magnitude
• Act in opposite directions
Object A exerts force on object B
FA on B
Object B exerts force on object A
FB on A
Are moving forces balanced?
Forces are balanced when they are not moving
What are the two types of forces?
Contact and non-contact forces
Define contact forces
Results when interacting objects are touching. Physical contact
What does contact forces include?
Friction, tension, and compression
Which type of force is action reaction?
Contact forces
Define friction
The force that opposes the motion of an object and which acts parallel to the surface
Define tension
The stretching force that is exerted by a rope, string or wire when it is pulled by a force.
Define compression
The force that pushes or squeezes something into a smaller space.
Define non-contact forces
Act over a distance and occur when two interacting objects are not in physical contact with each other
What does non-contact forces include?
Magnetic, electrostatic and gravitational
What is another name for non-contact forces?
Field forces
What is magnetic force exerted by?
Any magnet
What is magnetic force experienced by?
Any magnetic material
What type of force is magnetic?
Attraction/Repulsion
What is electrostatic force exerted by?
Any charged object
What is electrostatic force experienced by?
any charged or neutral object
What type of force is electrostatic?
Attraction/Repulsion
What is gravitational force exerted by?
Any object with mass
What is gravitational force experienced by?
Any object with mass
What type of force is gravitational ?
Attraction
What is a magnetic force?
A magnetic force is a force that two magnetic materials exert on each other over a distance.
What do magnets attract?
Other magnetic materials
What material are magnetic substances?
Iron, cobalt, nickel
How many poles do magnets have?
All magnets have two poles: a north pole and a south pole.
Define magnetic fields
Regions in space around magnetic objects where magnetic force is experienced.
Which poles attract?
Opposite poles attract
Which poles do not attract?
like poles repel
What type of magnet is the earth?
The Earth can be considered as one large bar magnet,
with a south pole and a north pole.
Why will objects experience magnetic force?
The Earth has a magnetic field around it, therefore when placed within this field, objects will experience a magnetic force.
What is the magnetic north pole of a compass is attracted to?
The geographical North Pole of the Earth.
What is the North pole actually?
South pole of the Earth’s magnet.
Define electrostatic force
An electrostatic force is a force that two electrically
charges objects exert on each other over a distance.
When does an electrostatic field exist?
An electrostatic field exists around any charged
object, and another object placed in that fields will
experience a force.
What happens when certain materials are rubbed together?
They can acquire an electrostatic charge as a result of
the loss or gain of electrons.
What has a gravitational field around it?
Any large object (planet, the sun, the moon)
What will experience gravitational attraction?
any object placed in that field will experience a force of attraction.
What does the magnitude of the gravitational force of attraction between two objects depends on?
The mass of the objects
The greater the distance
What does objects with a larger mass exert?
a greater force of attraction
What type of force does the greater the distance between the two objects create?
the smaller the force
What is gravity?
‘Gravity’ is the gravitational force of attraction that the Earth exerts on all objects.
Which direction does gravity act?
vertically downwards, towards the centre of the Earth.
What is gravity also called?
Weight
Define weight
Weight is the gravitational force that the Earth exerts on any object on or near its surface.
Is mass and weight the same thing?
No
Unit for weight
Newton
What does weight depend on?
Depends on where the object is (variable)
How is weight measured?
Measured using a spring scale/balance
Define mass
A measure of the quantity of matter possessed by an object
Unit for mass
Kilogram
What does mass depend on?
Constant regardless of where the object is
How is mass measured?
Measured using a triple beam balance
What do balances determine?
A balance determines mass by balancing an unknown mass against a known mass
How do scales determine weight?
Most weighing scales use sets of springs to measure the force acting on a mass to determine weight.
Formula for gravitational force
Fg = mg
What is the acceleration due to gravity for earth?
9,8
What is the acceleration due to gravity for moon?
1,6
