Chapter 5A: Forces Flashcards
How do you calculate the speed on a distance time graph?
The gradient of the line
What is the formula for acceleration?
Change in velocity (m/s) / Time taken (s)
How do you calculate the distance traveled on a velocity time graph?
The area under the graph
How do you calculate the acceleration on a velocity time graph?
The gradient of the line
What is the SUVAT equation?
final velocity^2 (m/s) - starting velocity^2 (m/s) = 2 * acceleration (m/s) * distance (m)
Why do feathers fall slowly?
The air resistance on them is close to their weight
What does the air resistance depend on?
The area and the speed
Why do objects reach terminal velocity?
Their weight is balanced by the air resistance
What is Newton’s 1st law?
When the resultant force acting on an object is 0, the object will not accelerate
What is Newton’s 2nd law?
When there are unbalanced forces acting on an object, it will accelerate
What is the equation that links mass to acceleration and force?
Force (N) = Mass (kg) x Acceleration (m/s^2)
What is inertia?
A measure of how difficult it is to change an object’s motion (inertial mass = force * acceleration)
What is Newton’s 3rd law?
Every force has a paired equal and opposite force?
What is momentum?
The product of mass and velocity. It’s a vector
What is the equation for momentum?
momentum (kgm/s) = mass (kg) * velocity (m/s)
What is the equation that links mass to force and acceleration?
force = (change in momentum) / time
Why do cars have crumple zones?
So that by buckling, they increase the impact time, decreasing the force
Why do cars have seatbelts?
Because in the time it takes for the crumple zone to buckle, you’ll fly forwards into something
What is the law of conservation of momentum?
When two objects collide, they have the same momentum as before the collision
What is a closed system?
A system with no external forces acting on it
How do you calculate the new speed of two objects after they collide?
New speed = (combined momentum) / (combined weight). Remember that since momentum is a vector, things moving relatively backwards have negative momentum
What is the formula for kinetic energy?
(mv^2)/2
What is the formula for work done?
Work done (J) = Force (N) * Distance (m)
Describe a parachutist’s descent
After jumping, he accelerates at 9.8m/s^2, but the effects of air resistance eventually slow his acceleration until he reaches terminal velocity (the air resistance is the same as his weight). After opening his parachute, the increased surface area causes increased air resistance, meaning he continues falling at a lower terminal velocity
