5.4 Moments, levers and gears Flashcards
What is a scalar quantity?
A scalar quantity has magnitude (size) only. Examples include:
* speed
* mass
* time
* energy
Scalar quantities are not affected by direction.
What is a vector quantity?
A vector quantity has magnitude and direction. Examples include:
* displacement
* velocity
* acceleration
* force
* momentum
Vector quantities provide information about both size and direction.
What is a contact force?
A contact force occurs when two objects touch each other. Examples include:
* friction
* normal contact force
* tension
* air resistance
These forces require direct interaction between the objects.
What is a non-contact force?
A non-contact force does not require two objects to touch each other. Examples include:
* gravity
* electrostatic force
* magnetism
Non-contact forces act over a distance.
What is Newton’s third law?
Newton’s third law states: ‘Every action has an equal and opposite reaction.’
This means if object A exerts a force on object B, then object B exerts an equal and opposite force on object A.
What is weight?
Weight is the gravitational force of attraction you experience because you are in the Earth’s gravitational field. It is measured in Newtons (N).
Weight is a force and is different from mass.
How is weight measured?
Weight is measured using a calibrated spring balance (Newton meter).
This device measures the force exerted by gravity on an object.
How would we calculate the weight of an object?
Weight = mass × gravitational field strength
W = mg
Where:
* Weight (Newtons, N)
* Mass (kilograms, kg)
* Gravitational field strength (Newtons per kilogram, m/s)
The weight and mass of an object are directly proportional.
What is the centre of mass of an object?
The centre of mass is a single point where the weight of an object may be considered to act.
It is the point where the mass of the object is concentrated.
What is a resultant force?
A resultant force is a single force that can replace two or more forces acting on an object.
It simplifies the analysis of forces acting on an object.
How do you calculate the size of a resultant force when two (or more) forces act along the same line?
If the forces act in the same direction, add the forces. If in opposite directions, subtract the smallest from the largest.
This results in the net force acting on the object.
How do you calculate the size of a resultant force when two forces act at right angles?
Draw a scale diagram to create a parallelogram (rectangle) with the two forces. Measure the resultant force’s length and direction.
Use a ruler for length and a protractor for angle measurement.
What does it mean to resolve a force into two components?
Resolving a force means splitting it into two components: one acting vertically and one acting horizontally.
This is often done using Pythagorean theorem and trigonometry.
How can you resolve the force of weight into two components when an object is on a ramp?
Weight can be split into one component parallel to the ramp and one component normal (perpendicular) to the ramp.
This helps in analyzing forces acting on inclined surfaces.
Why does the moon orbit the Earth?
The moon orbits due to a resultant force acting towards the Earth caused by Earth’s gravitational field, resulting in circular motion.
There is also an equal force acting on the Earth due to the moon’s gravitational field.
What is a moment?
A moment is the turning effect of a force causing an object to rotate.
Moment = force × perpendicular distance from pivot.
Units are Newton metres (Nm).
What is the principle of moments?
The principle of moments states that if an object is balanced, the sum of all clockwise moments equals the sum of all anticlockwise moments.
This is fundamental in static equilibrium analysis.
What is a gear?
Gears are devices used to transmit the rotational effects of forces from one place to another.
An example is a bike gear transmitting pedal rotation to the wheels.
How do gears work?
Cog A transmits its moment to cog B at the point of contact. Due to different sizes, the turning effect of cog B differs from cog A.
This difference is due to the varying perpendicular distances from the pivot.
