Forces and Motion Flashcards
Average Speed equals
Total Distance/Total Time
Is Speed a scalar quantity?
Yes
Examples of Scalar Quantities
Distance, Speed, Time, Energy
Is Velocity a scalar quantity.
No. It is a vector quantity as it has magnitude and direction.
Acceleration equals
Change in velocity/time
v squared =
u squared + 2as (where s is displacement)
Examples of vector quantities
Displacement, Velocity, Acceleration, Force
On a Distance - Time graph, the gradient is equivalent to
Velocity
On a Velocity - Time graph, the gradient is equivalent to
Acceleration
On a Velocity - Time graph, the area under the graph is equivalent to
Distance travelled
Newton’s First Law
an object has a constant velocity unless acted on by a resultant force
Newton’s Second Law
F = ma
Newton’s Third Law
Every action force has an equal and opposite reaction force
Mass measures
the amount of matter in an object
Weight =
Mass x Gravitational field strength
Explain what happens (in terms of forces and acceleration) as an object is released from rest and then falls under gravity
- Object begins to accelerate as the force downwards due to gravity is greater than the force opposing motion due to air resistance.
- As the speed increases, so the air resistance increases.
- When the air resistance is equal to the force due to gravity then the forces are in equilibrium and the body will move at a constant velocity.
Thinking distance is
the time between seeing the hazard and starting to brake
Braking distance is
the time between pressing the brake pedal and stopping
Stopping distance is
Thinking distance + Braking distance
Thinking distance depends on
- Speed
- Alertness (e.g. tiredness, alcohol)
Braking distance depends on
- Speed
- Mass of vehicle
- Road conditions
- Tyres
Deformations is
when a force produces a change in size or shape of a body
Elastic deformation is
when the body returns to its original size and shape after deformation
Hooke’s Law
Force = Spring constant x Extension (F = kx)
On a Force - Extension graph of a spring
- The initial straight part is the Elastic Region
- The end of the initial straight part is the limit of proportionality
- The curved part is the plastic region
- The end of the curved part is when the body/spring fractures
Moment equals
Force x Perpendicular distance from the pivot
Moment is a measure of
turning effect
Moment is measured in
Nm
If the sum of the clockwise moments equals the sum of the anticlockwise moments, then the body is
In equilibrium
Momentum equals
Mass x Velocity
Momentum is measured in
kgm/s
Force equals
change in momentum/time
To increase safety in a car
force is reduced by increasing time for a given momentum change - e.g. car seat belt or air bag
The six contact forces are
- Friction
- Air-resistance
- Tension
- Spring force
- Applied force
- Normal force
FAT SAN
The three action at a distance forces are
- Gravitational
- Electrical
- Magnetic
In a collision, momentum is always
conserved
