physics - forces Flashcards
(19 cards)
What is a scalar quantity?
A scalar quantity has magnitude (size) only. Examples include:
* speed
* mass
* time
* energy
Scalar quantities do not have a direction associated with them.
What is a vector quantity?
A vector quantity has both magnitude and direction. Examples include:
* displacement
* velocity
* acceleration
* force
* momentum
Vector quantities are represented by arrows where the length indicates magnitude and the direction indicates 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
Contact forces require physical interaction between 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 at a distance.
What is Newton’s third law?
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 due to the Earth’s gravitational field. It is measured in Newtons (N).
Weight is a force and varies with the gravitational field strength.
How is weight measured?
Weight is measured using a calibrated spring balance (Newton meter).
This instrument provides a direct measurement of force.
How would we calculate the weight of an object?
Weight = mass × gravitational field strength (W = mg)
Weight (Newtons, N), Mass (kilograms, kg), Gravitational field strength (Newtons per kilogram, m/s).
What is the centre of mass of an object?
The centre of mass is the point where the weight of an object can be considered to act.
It is also the point where the mass of the object is concentrated.
What is a resultant force?
The resultant force is a single force arrow that replaces two or more forces acting on an object.
It represents the net effect of all the forces acting.
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 them. If they act in opposite directions, subtract the smallest from the largest.
This gives 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), then measure the resultant force’s length. Use a protractor to find the angle.
Pythagorean theorem can also be applied for calculation.
What does it mean to resolve a force into two components?
To resolve a force means to split it into two components: one acting vertically and one acting horizontally.
This is typically done using trigonometry.
How can you resolve the force of weight into two components when an object is on a ramp?
The weight can be split into one component parallel to the ramp and one component normal to the ramp.
This is essential for analyzing motion on inclined surfaces.
Why does the moon orbit the Earth?
The moon orbits due to a resultant force acting towards the Earth from the Earth’s gravitational field, causing 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 caused by a force. It is calculated as Moment = force × perpendicular distance from pivot.
Units are Newton metres (Nm).
What is the principle of moments?
If an object is balanced, the sum of all clockwise moments equals the sum of all anticlockwise moments.
This principle is used in static equilibrium analysis.
What is a gear?
Gears are devices used to transmit the rotational effects of forces from one place to another.
For example, bike gears transmit the effect of pedaling to the wheels.
How do gears work?
Cog A transmits its moment to cog B at the point of contact, resulting in a different moment due to size differences.
The relationship between moments is expressed as momentB > momentA.
