Forces, Movement, Shape, and Momentum Flashcards
What are the effects of forces between bodies?
Change in speed (acceleration or deceleration) due to applied or removed forces.
Change in shape (compression, stretching, bending) caused by stress or strain.
Change in direction (turning effect) when a force is applied at an angle.
Forces can be balanced (resulting in no motion change) or unbalanced (causing acceleration).
What are the different types of forces?
Gravitational force: Attraction between masses, responsible for weight.
Electrostatic force: Force between charged objects, like attraction or repulsion.
Magnetic force: Force between magnets or moving charges.
Frictional force: Opposes motion between two surfaces, can cause heat.
Normal force: The support force exerted by a surface perpendicular to an object.
What is Newton’s Third Law of Motion?
For every action, there is an equal and opposite reaction.
Forces always occur in pairs acting on different objects.
Example: A rocket pushes gases downward, and gases push the rocket upward.
What is the equation for the moment of a force?
Moment = Force × Perpendicular distance from pivot
Measured in Newton-metres (Nm)
Where does the weight of a body act?
Through its centre of gravity, the point where weight appears to act.
What is the principle of moments?
The principle of moments states that for an object to be in equilibrium, the total clockwise moment must equal the total anticlockwise moment.
If these moments are not equal, the object will experience a rotational force and begin to turn.
This principle is used in simple systems of parallel forces acting in one plane, such as levers, beams, and bridges.
It ensures stability in structures and machinery by balancing forces effectively.
Example: If a uniform beam is supported at two ends, the forces at the supports vary depending on the position of a load placed along the beam.
How do the upward forces on a supported beam vary with the position of a load?
The closer the load is to a support, the greater the force at that support.
If the load is at the center, both supports share equal forces.
If the load is closer to one end, that support bears more force.
How do vector quantities differ from scalar quantities?
Vector: Has magnitude and direction (e.g., velocity, force, displacement)
Scalar: Has only magnitude (e.g., speed, mass, time)
Vectors require both magnitude and direction to be fully described.
Why is force a vector quantity?
It has both magnitude (size of force) and direction (which way it acts).
Example: A 10N force to the right is different from a 10N force to the left.
How do you calculate the resultant force of forces that act along a line?
If in the same direction: Add the forces.
If in opposite directions: Subtract the smaller force from the larger.
The resultant force determines acceleration or movement.
What is friction?
A force that opposes motion between two surfaces.
Can produce heat and cause wear on surfaces.
Can be reduced with lubrication or smooth surfaces.
What is the equation for force, mass, and acceleration?
Force = Mass × Acceleration (F = ma)
What is the equation for weight?
Weight = Mass × Gravitational field strength (W = mg)
What is stopping distance?
The sum of thinking distance and braking distance.
Thinking distance: Distance traveled before reacting.
Braking distance: Distance traveled while slowing to a stop.
What factors affect stopping distance?
Speed: Higher speed increases both thinking and braking distance.
Mass of the vehicle: Heavier vehicles take longer to stop.
Road and weather conditions: Wet or icy roads reduce friction.
Brake condition: Worn brakes increase braking distance.
Driver’s reaction time: Fatigue, alcohol, and distractions slow reaction.
What forces act on a falling object?
Weight (downwards, caused by gravity).
Air resistance (upwards, increasing with speed).
Resultant force = Weight - Air resistance (affects acceleration).
Why does a falling object reach terminal velocity?
Air resistance increases as speed increases.
Eventually, air resistance equals weight, so no resultant force acts.
The object then falls at a constant velocity (terminal velocity).
Describe an experiment to investigate extension with applied force.
Set up a clamp stand with a spring, wire, or rubber band.
Measure the original length using a ruler.
Add weights incrementally and measure new lengths each time.
Record force and extension, plotting a force-extension graph.
Identify the limit of proportionality where Hooke’s Law stops applying.
What is Hooke’s Law?
Extension is directly proportional to applied force (F = kx) within the elastic limit.
Beyond the elastic limit, permanent deformation occurs.
Used in springs, elastic bands, and engineering materials.
The initial linear region of a force-extension graph follows Hooke’s Law.
What is elastic behaviour?
Ability of a material to return to its original shape after forces are removed.
What is the equation for momentum?
Momentum = Mass × Velocity (p = mv)
How do safety features use momentum principles?
Airbags, seatbelts, and crumple zones increase the time of impact.
This reduces the force experienced (since F = change in momentum / time).
Reducing force helps prevent serious injuries.
What is the principle of conservation of momentum?
Total momentum before collision = Total momentum after collision (if no external force acts).
How can momentum conservation be used to calculate unknown values?
Use p = mv for each object before and after a collision.
Solve for the unknown variable.
Used in collision and explosion calculations.
What is the relationship between force, change in momentum, and time?
Force = (Change in momentum) / (Time taken).
F = (mv - mu) / t.
