Unit 5 - Forces Flashcards
What is a contact force?
A force that occurs when objects are physically touching eg friction and air resistance
What is a non-contact force?
A force that occurs when objects are not physically touching eg magnetism and gravity
What is the difference between scalars and vectors?
Scalar - a quantity that only has magnitude eg speed
Vector - a quantity that has magnitude and a direction applied to it eg velocity
What does it mean if there is no resultant force?
There is no acceleration (constant velocity)
What is the equation for weight?
Weight (N) = mass (kg) x gravitational field strength (N/kg)
What is work done?
Energy transferred by a force
What is the equation for work done?
Work done (J) = Force (N) x distance (m)
What is Hooke’s law?
Force and extension are directly proportional
What is the equation for the force of a spring?
Force (N) = spring constant (N/m) x extension (m)
What is a moment?
A turning force such as using a spanner
What is the equation for a moment?
Moment (Nm) = Force (N) x distance from pivot (m)
What is the principle of moments?
When the sum of the total clockwise moments = the sum of total anticlockwise moments, a system is in equilibrium (it won’t turn)
How can we increase a moment?
Moments can be increased using gears by driving a large year with a smaller one
What is the equation for pressure?
Pressure (N/m² or Pa) = Force (N) ÷ Area (m²)
What causes pressure underwater?
The weigh of the column of water above an object pushing down on it
What is the equation for pressure in fluids?
Pressure (Pa) = height (m) x density (kg/m³) x g (N/kg)
What causes pressure in a gas?
The particles colliding with the walls of its container, exerting a force on them.
How can we increase pressure in a gas?
-Decrease volume (more collisions per second with container)
-Increase volume of gas particles (more frequent collisions)
-Increase temperature (more frequent collisions and collisions with more momentum so greater force)
How does air pressure change with altitude?
Higher altitude means lower density in the atmosphere, causing lower pressure
What does the gradient of a distance/displacement-time graph give you?
Speed/velocity
What does the gradient of a speed/velocity-time graph give you?
Acceleration (m/s²)
What does the area under a velocity-time graph give you?
Displacement
What are Newton’s equations of motion?
S - displacement (m)
U - initial velocity (m/s)
V - final velocity (m/s)
A - acceleration (m/s²)
T - time (s)
What is the third equation of motion?
V² - U² = 2as
What is Newton’s 1t law?
If no resultant force acts on an object, its motion will be constant.
What is inertia?
The tendency for an object’s motion to stay constant unless acted on by a resultant force
What is Newton’s 2nd law?
Force (N) = mass (kg) x acceleration (m/s²)
What is Newton’s 3rd law?
For every action (force) there is an equal and opposite reaction (force)
What is the stopping distance?
Stopping distance = thinking distance + braking distance
What factors affect thinking distance?
-Speed
-Distractions
-Alcohol
-Drugs
-Tiredness
What factors affect braking distance?
-Speed
-Condition of brakes, tyres and road
-Weather conditions
What is the equation for momentum?
momentum (kgm/s) = mass(kg) x velocity (m/s)
What is the conservation of momentum/
In any collision in a closed system, total momentum is always conserved
What is the relationship between force and momentum?
Force is a measure of the rate of change of momentum. The longer the time over which momentum is lost or gained, the lower the force exerted and vice versa
How can we reduce the force of a crash?
Increase collision time, causing momentum to be lost over a longer time. We can increase collision times by using air bags, seat belts and crumple zones
