Chap 8 Flashcards
what is force
force is a pull or a push upon an object
Force may exist in various forms/types such as :
gravitational force
weight
normal force
frictional force
elastic force
buoyant force
Explain gravitational force
-the force that points towards the centre of the earth
-causes all object that r thrown upwards to fall back to earth
explain normal force
-force produced when an object is in contact w a surface
explain weight
- defined as the gravitational force acting on it
explain elastic force
- exists when a material is stretched or compressed
explain buoyant force
- the thrust force acting on an object that is floating on the surface of a fluid
explain frictional force
- the force that resists movement between two surfaces that r in contact w each other
-acts in the opposite direction of the motion
Characteristic of force
- is a vector quantity that has magnitude n direction
-has point of application
-magnitude is the quantity or value of a measuremt
S.I. unit of force
Newton (N)
How do we measure force
- using a spring balance
- spring balance operates based on the principle of spring extension
100g has a weight of _____ N
1kg has a weight of ____ N
1 N
10N
Newtons third law states:
that for every action force, there is a reaction force of the same magnitude but in the opposite direction
Force cannot be seen but
its effects can be felt
force can change the:
shape, size and motion of the object
state the effects of force
-moving stationary object
- stopping a moving object
- changing the speed of an object that is in motion
-changing the direction of motion of an object
-changing the shape and size of an object
Explain buoyant force
-object will only float if the buoyant force acting on it is enough to support its weight
-will submerge if not enough
Actual weight means
weight of an object in the air
apparent weight means
weight of an object immersed in fluid
Explain how does an object float in fluid
-buoyant force pushes the object up to the surface bcuz the object is less dense than the liquid is when in the liquid
Why are cargo ships marked with plimsoll lines
- for safety purposes
- density of sea water is diff in diff parts of the world cuz of the temp and concentration in salt
- plimsoll lines will help to determine the safe level for a ship to stay afloat
what is a lever
a bar that rotates on a fixed point
lever is made up of 3 parts, which are:
- Effort
- Load
- fulcrum
Explain the 3 parts of a lever
Effort: force applied on the bar
Load: Object to be moved
Fulcrum: Fixed support point
Explain purposes of lever
- allows us to do work easily
- allows us to use minimal force to do work
levers are classified into 3 types:
-first class
-second class
-third class
When does a lever classify as a first class lever
- fulcrum is between lad and effort
when does a lever classify as a second class lever
-load is between fulcrum and effort
when does a lever classify as a third class lever
- effort is between fulcrum and load
WHat does moment of force mean
- the turning effect produced when a force acting on an object can rotate the object at a fixed point
Elaborate more abt moment of force:
- allows us to do work easily
- depends on the force applied & the perpendicular distance of the fulcrum to the force
Force is always towards:
where we pull
Method to calculate force:
Moment of force = Force (N) x perpendicular distance from the pivot to the force (m)
Simplified: MOF= (N x M)
Unit for moment of force is
newton metre ( N m)
moment of force has 2 directions
- either clockwise or anticlockwise
moment of force will increase if:
- magnitude of force increases, by applying a greater force
- perpendicular distance from pivot to effort increases
Greater moment of force is produced when:
force is applied at a greater distance from the turning point
Formula to solve daily life problems involving levers
Load (N) x Distance of load from fulcrum (m) = Effort (N) x Distance of effort from fulcrum (m)
simplified: N x distance of load (m) = N x distance of effort (m)
S.I unit for pressure
pascal (Pa)
1 Pa equals
1 newton per square metre ( N m-² )
Pressure =
Force (N) / Surface area (m²)
The smaller the _______, the _______ it is for that thing to be pressed
-surface area
-easier
pressure defined as
force per unit area
Kinetic theory of gas states:
air molecules always move about freely and collide with the walls of its container
Whats air pressure
- the force that pushes against the walls and is produced as a result of the frequency of collision between the air molecules and the walls of the container
Factors that affect air pressure
-volume
-temp
what happens when a close container is compressed
-volume in the container is reduced
- causes the air particles to collide more frequently w the walls of the container
- air pressure in the container increases
What happens when air temp in a closed container increases
- air particles move faster
- causes air particles to collide w the walls of container more frequently and w a greater force
-air pressure increases
the lower the temp, the ____ the movement of air particles
-slower
the higher the temp, the ___ the movement of air particles
- faster
What causes a packet to compress when drink is sucked out
- the drink inside becomes a partial vacuum
-air pressure inside decreases
-the higher the air pressure outside will press onto the packet and compress it
what is the air pressure outside called
atmospheric pressure ( aka the pressure exerted by the atmosphere on the surface n all objects on earth )
examples of application of the concept of air pressure in daily life
-plunger
-magdeburg hemisphere
-straw
-syphon
-syringe
-vacuum cleaner
atmospheric pressure ____ as altitude increases
-decreases
Explain gravitational attraction
- air molecules closer to the surface of the earth r pulled tgt by the gravitational attraction causing a rise in pressure
- at higher altitudes, air molecules are less affected by the gravitational attraction, so air becomes less heavy n expands easily
-causes a low atmospheric pressure at high altitude
Liquid pressure decreases as the:
depth of liquid decreases
Liquid has more pressure at the _
bottom
