Chapter 4 Forces Flashcards
Force
Force = mass x acceleration
Weight
Weight = mass x g
Define centre of mass
The place at which an which if an external force is applied will not rotate and will accelerate linearly.
Define tension
The force within a stretched cable or rope
Define centre of gravity
The place at which all weight appears to act.
What is a Newton?
Unit for force.
1 Newton is the force required to accelerate a 1Kg object at 1ms^-2.
Terminal velocity
Initially all force is in weight.
As the object starts to accelerate the drag increases resulting in a smaller resultant force.
The drag increases more until it is equal to the weight and so the resultant force is 0 and so is the acceleration.
The velocity is constant and this is called terminal velocity.
Moment of a force
Moment = force x perpendicular distance from the line of action of the force from the pivot or axis of rotation from pivot.
The principle of moments
The principle of moments states that an object in rotational equilibrium, the sum of the clockwise moments will equal the sum of the anti-clockwise moments around the same fixed point.
How would you find centre of mass in a gravitational field?
- Set up equipment.
- Allow plumbline and shape to hang freely.
- Allow both to settle and mark dots along the length of the plum line on the card by holding them gently together.
- Repeat at a new point roughly 90 degrees from first point.
- Connect up your lines with a ruler and mark where they cross, this is your centre of mass.
Archimedes principle
The upthrust acting on the object whether fully or partially submerged is equal to the weight of the fluid it disperses.
Couple
When an object experiences 2 equal but opposite forces whose lines of action are separated by a perpendicular distance.
Torque of a couple
Force of one of the parts of the couple x the perpendicular distance between the lines of action.
Density
Mass/Volume
Pressure
Pressure is the normal force exerted per unit cross-sectional area. You can use pressure = force / area
