Chapter 4: Forces in Action Flashcards
mass
The amount of matter in an object
what does a greater mass lead to?
greater inertia
weight
force experience by mass due to a gravitational force
centre of mass
single point where the whole weight of an object appears to act
How do you find the centre of gravity of an object?
1) hang object freely from a string
2) vertical line downwards from point of suspension - plumb bob
3) Hang object from different point and draw another vertical line
4) Centre of gravity is where the two points meet
What are the types of forces?
- normal contact force
- tension
- friction
- upthrust
normal contact force
surface exerts equal but opposite force on an object
tension
pulling force on an object from either end of a string
friction
force acting opposite to motion
upthrust
submerged object experiencing upwards force
free body diagram
all forces acting on a single object
net force
sum of all the forces acting on an object
How do you accelerate an object?
Having a non-zero resultant force
What are three ways you can find the resultant force of vectors?
- pythagoras
- sine rule
- cosine rule
equilibrium
all forces are balanced and cancelled out
triangle of forces
forces form a closed loop when joined tip-to-tail
What are the sum of forces when an object is in equilibrium?
0
moment
turning effect of a force around a pivot
What factors affect moment?
-size of force
-distance from pivot
principle of moments
if a body is in equilibrium, the sum of the clockwise moments = sum of the anticlockwise moments
Do you need to consider the weight of the turning object in calculations?
only if the line of action is not directly over the pivot
What makes an object topple over?
line of action falls outside the base area, a resultant moment occurs, causing it to fall
What does it mean if an object has a high centre of mass?
smaller base area
What makes an object stable?
- low centre of mass
- wide base area
What happens in levers?
effort force acts against the load, causing a rigid rotation
What happens when an object’s centre of mass is close to a support?
stronger force acts on the support
couple
pair of forces of equal size which act parallel to each other but in opposite directions
torque
moment of a couple
torque equation
M = Fd
Equation for moment
M = F x perpendicular distance from a pivot
Describe what happens when a resultant force acts on a body with mass?
Body will accelerate in the direction of the resultant force
drag
frictional force that opposes motion as an object moves through a fluid
terminal velocity
forces acting on a falling object become balanced so the resultant force is 0, acceleration is 0 and object moving at maximum velocity
density
mass per unit volume of a substance
a measure of a substance’s “compactness”
density equation
density = mass / volume
pressure
amount of force applied per unit area
pressure equation
pressure = force / area
What happens in a fluid regarding pressure?
particles collide with the object, exerting a force over a specific area
what happens in a denser fluid?
more particles in a denser volume, more particles collide and a larger force is exerted, causing a higher pressure
What happens as the depth increases?
number of particles above a point increase, weight of the particles add pressure
pressure in fluid equation
depth x density x gravitational field strength
upthrust
upwards force that fluids exert on objects that are completely or partially submerged in a fluid
equation for upthrust
(h2 - h1) x density x g x area
archimedes’ principle
when a body is completely or partially submerged in a fluid, it experiences an upthrust equal to the weight of the fluid it has displaced
what determines if an object floats or sinks?
average density
What makes an object float?
lower density than fluid object will only displace as much volume of water that weighs as much as the object
What makes an object sink?
object more dense than fluid
weight of water < weight of object
upthrust < weight
what suitable measuring instrument would you use to measure the diameter of the ball?
calliper or micrometer
