P8. Forces in Balance Flashcards
What is a scalar quantity?
A quantity that only has a magnitude
A quantity that isn’t direction dependent
What is a vector quantity?
A quantity that has both a magnitude and an associated direction
How can a vector quantity be drawn and what does it show?
As an arrow
The length of the arrow represents the magnitude
The arrow points in the associated direction
What is a force?
A push or pull acting on an object due to an interaction with another object
What are the two categories that all forces can be split into?
- Contact forces (objects touching)
- Non-contact forces (objects separated)
Give three examples of contact forces.
- Friction
- Air resistance
- Tension
Give three examples of non-contact forces
- Gravitational forces
- Electrostatic forces
- Magnetic forces
Is force a vector or a scalar quantity?
Vector because it has both a magnitude and an associated direction
Give three examples of vector quantities
- Velocity
- Displacement
- Force
Give three examples of scalar quantities
Temperature
Time
Mass
Speed
Distance
Energy
What is weight?
The force that acts on an object due to gravity and the object’s mass
What quantities does weight depend on?
Weight = mass × gravitational field strength
The object’s mass
The gravitational field strength at the given position in the field
What is the unit used for weight?
Newton (N)
What is the unit used for gravitational field strength?
N/kg
What is meant by an object’s centre of mass?
The single point where an object’s weight can be considered to act through
What piece of equipment can be used to measure an object’s weight?
A calibrated spring-balance or newton-meter
What is meant by an object’s centre of mass?
The single point where an object’s weight can be considered to act through
What does it mean if a force is said to do ‘work’?
The force causes an object to be displaced through a distance
What is the equation used to calculate work done?
Work done = Force × Distance
What distance must be used when calculating work done?
It must be the distance that is moved along the line of action of the force
Under what circumstance is 1 joule of work done?
When a force of 1 Newton causes a displacement of 1 metre
How many Newton-metres are equal to 1 joule of energy?
1 Nm = 1 J
How much work is done by the force acting on the below object over a distance of 5m?
10 × 5 = 50Nm
= 50 J
What occurs when work is done against frictional forces?
A rise in temperature of the object occurs
Kinetic energy is converted to heat
Why does air resistance slow down a projectile?
The object does worm against the air resistance
Kinetic energy is converted in to heat, slowing down the object
Explain the relationship between the force applied and the extension of an elastic object
The extension is directly proportional to the force applied, provided that the limit of proportionality is not exceeded
What is meant by an inelastic deformation?
A deformation which results in the object being permanently stretched
The object doesn’t return to its original shape when the force is removed
State the equation relating force, spring constant and extension
Force = Spring Constant × Extension
What type of energy is stored in a spring when it is stretched?
Elastic Potential Energy
What can extension be replaced with in the equation for spring force?
Compression
What is the alternative name for the turning effect of a force?
A moment
State the equation used to calculate the moment of a force
Moment of force = Force × Distance
What distance measurement is used when calculating a moment?
The perpendicular distance from the pivot to the line of action of the force
If an object is in equilibrium, what can be said about the moments acting on the object?
The clockwise moment are equal to the anticlockwise moments
What three parts make up a lever system?
- Load
- Effort
- Pivot
How can a lever be used as a force multiplier?
If the distance between the effort and pivot is greater than the distance between the pivot and load, the force applied on the load is greater than the effort force. This is since the moment on both the effort and load must be the same
Give an example of when a level may be used to multiply a force
A wrench, which has a long handle so that the force applied by the user is multiplied
What determines the moment of a gear wheel?
The size of the wheel
Describe the moment and speed of a larger gear being driven by a smaller gear
The larger wheel will rotate more slowly but will also produce a larger moment
