Forces Flashcards
(13 cards)
Changes in motion of a skydiver in terms of forces
Initially air resistance is less than gravity so skydiver accelerates
Acceleration causes air resistance to increase
Resultant force decreases to zero
So skydiver falls at terminal velocity
Explain why jumping from 39,000 metres allowed the skydiver to reach a much higher speed than a skydiver jumping from 4000 metres
The higher altitude the less dense the air
So the air resistance on the skydiver falling from 39000m was less
So the skydiver was able to accelerate for longer before reaching terminal velocity
Explain why atmospheric pressure decreases with increasing altitude
Air molecules colliding with a surface create pressure
At increasing altitude fewer air
So number of collisions with a surface decreases molecules
What is the difference between distance and displacement
Distance is a scalar and displacement is a vector
Explain why the stopping distance from the car increases if the driver is very tired
The reaction time will increase
Increasing the thinking distance
What property of a liquid enables a hydraulic brake system to work
Liquids are virtually incompressible
Centre of mass definition
The single point where an objects weight can be considered to act through
Three contact forces
Three non contact forces
Friction,air resistance, tension
Gravitational forces, electrostatic forces , magnetic forces
Why does air resistance slow down a projectile
The object does work against the air resistance
Kinetic energy is converted in to heat, slowing down the object
Explain why an object with a density greater than that of water can never float
Upthrust is equal to the weight of the displaced fluid
Of the density of the object is high there would not be enough volume displaced to produce an Upthrust larger than the objects weight so it will sink
Typical value for human walking speed
Typical value for human running speed
Cycling speed
1.5m/s
3m/s
6m/s
Inertia
The tendency of an object to continue in its state of rest or uniform motion
