Chapter 3.2 - Forces in Action Flashcards
Equation for weight
W=mg
Tension
A force experienced by a string or wire that is being pulled
Normal contact force
A force that acts perpendicular to the point of contact between two surfaces
Upthrust
The upward force that a liquid or gas exerts on a body due to the liquid or gas being displaced
Friction
A force that occurs between two surfaces that opposes motion. It is a result of intermolecular forces.
What you show on a free body diagram (3)
- The bodies
- The directions of each force
- The value of each force
Fluid
A liquid or a gas
Drag
The frictional force experienced by an object travelling through a fluid
Does friction depend on velocity
no sir
Does drag depend on velocity
o yes
How is drag related to velocity
D = kv^2
Factors affecting drag (4)
- Density of fluid
- Coefficient of drag
- Cross sectional area of object
- Velocity
The motion of an object falling in the presence of drag
- Initially accelerates because force of gravity acts downwards and there is minimal drag
- As speed increases the upwards force of drag increases
- Eventually the force of weight is equal to the force of drag and the object no longer accelerates and is moving at its terminal velocity
What happens when a parachute is opened while falling at terminal velocity
The drag force increases due to the increased cross sectional area. This results in a net upwards force and therefore an upwards acceleration, which causes the skydiver to slow down. As they slow down the drag force decreases until a new terminal velocity is reached
Terminal velocity
The speed of an object at which the weight is equal to the drag
Experiment to determine terminal velocity of a body in a fluid
Set up a cylinder filled with fluid and wrap elastic bands around it at regular intervals. Drop a ball of known mass into the tube and time how long it takes to reach each elastic band. Towards the bottom the times should remain constant and this value is used to calculate terminal velocity
Equilibrium
The resultant force acting on an object is zero
How to find the resultant of two forces
Add them
Moment
The turning effect of a force
Equation for a moment
moment = force * perpendicular distance
Principle of moments
For a body to be in equilibrium, the sum of the clockwise components must equal the sum of the anticlockwise components
Couple
Pair of forces of equal size that act in parallel but opposite directions, resulting in a turning force (torque)
Equation for torque of a couple
T = (magnitude of one force) * (perpendicular distance between the forces)
Weight
Force experienced by a mass due to a gravitational field