3.2 Forces In Action Flashcards
What is the equation for force (F)
Force (N) = mass (kg) x acceleration (ms -2)
F = ma
What happens to the motion of an object with a resultant force acting on it
It will accelerate in the direction of the resultant force
What is weight (W) and state its unit
The gravitational force acting upon the object
Newtons (N)
What is the acceleration of free fall on earth (g)
9.81ms -2
What is friction
The force caused when two surfaces rub together
What is drag
The resistive force on an object travelling through a fluid (water / air)
Frictional force opposing motion
What is up-thrust
The upward buoyancy force acting on an object in a fluid
What is tension
The force within a stretched cable or rope
What is normal contact force
The force caused by an object resting against another, perpendicular to the plane of contact
What factors affect drag
- speed
- shape & texture
- density of the fluid
- cross sectional area (surface area affected)
What is the equation for drag
Drag (N) ∝ velocity2 (ms-1)
F(d) ∝ v2
What is the impact of drag in free fall
Reduce the resultant force of weight and the magnitude of downward acceleration
Drag increases until it is equal to weight (terminal velocity)
What is terminal velocity
When drag = weight in free fall
Resultant force is zero so acceleration is zero / velocity is constant
what is the moment of a force
the magnitude of the force
what is the equation for moment (M)
moment (Nm) = perpendicular distance (m) x force (N)
Moment = Fx
what is a couple
a pair of forces with equal magnitude and opposite direction that are applied to a body in parallel to each other
what do couples produce
a rotational force with no translational movement
what is the torque of a couple
the product of the magnitude of one of the forces x the perpendicular separation between the forces
what is the equation for torque
torque (Nm) = force (N) x distance (m)
torque = Fd
what is the principle of moments
when a body is in equilibrium the net force acting on it is 0N, and its net moment is also 0Nm
for a body in equilibrium, the sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about the same point
what is an objects centre of mass
- where the entire weight appears to act
- the point which the application of an external force produces motion in a straight line only with no rotation
- coincides with centre of gravity as long as the object is within an external gravitational field
Describe motion when force is applied to an object’s centre of mass
It only moves in a straight line
What is density (ρ) and state its units
Density is mass per unit volume
Measured in kilograms per cubic meter (kgm -3)
What is pressure (p) and state its units
The normal force exerted on a surface per unit cross sectional area
Pascal (Pa)
What is the equation for density
Density = mass / volume
ρ = mv
What is the equation for pressure
Pressure = force / cross sectional area
p = F / A
What is Archimede’s principle
The upthrrust exerted on a body immersed in fluid, whether partially orfullly submerged, is equal to the weight of the fluid that the body displaces.
