P10: Force and Motion Flashcards
What is Newton’s first law of motion?
If the resultant force on an object is zero and it is stationary, it will remain stationary, if it is moving, it will be moving at constant velocity
What causes an object’s velocity to change?
A resultant force
What is Newton’s second law of motion?
The acceleration of an object is proportional to the resultant force acting on the object and inversely proportional to the mass of the object
How does acceleration change with force?
The greater the force applied, the greater the acceleration
What is the formula for force in relation to acceleration?
F = ma
Force = mass * acceleration
(N) (Kg) (m/s²)
What is inertia?
The tendency of an object to continue in its state of rest or motion.
What is inertial mass?
A measure of how difficult it is to change the velocity of an object.
force needed to accelerate : acceleration produced
- a large inertial mass requires a greater force to produce the same acceleration
What is Newton’s third law?
Whenever two objects interact, the forces they exert on each other are equal and opposite.
What are the forces acting on a skydiver?
They fall due to gravity, and experience a resultant force acting downwards because the force of gravity is more than that of air resistance. As they fall, they experience friction with air molecules, acting upwards, at a certain point, air resistance balances the weight of the skydiver and reach a resultant force of 0. (moving at constant velocity - terminal velocity)
Why is a parachute nessesary for a skydiver?
Increases surface area to increase air resistance - air resistance is now greater than the weight - resultant force acting upwards, causing the skydiver to decelerate. Skydiver will fall at a lower terminal velocity, making it safe for them to hit the ground.
What is stopping distance?
The total distance travelled from when the driver first spots the obstruction to when the car actually stops
Thinking distance + braking distance = stopping distance
What is the thinking distance?
Distance travelled by the car during the driver’s reaction time
What is the braking distance?
Distance travelled from when the driver applies the breaks to when the car actually stops
How does the speed at which a vehicle is travelling at affect stopping distance?
Speed increases stopping distance
What factors influence reaction time/ thinking distance?
Fatigue
Alcohol
Drugs
Other distractions
What factors influence braking distance?
Icy road - reduces friction
Worn tyres - reduces friction
Worn brakes
What happens during braking?
A brake presses against the wheel, a force of friction now acts between the brake and the wheel. The kinetic energy of the car is now converted to thermal energy in the brakes - causing a temperature increase
Car slows down as it loses kinetic energy.
How does speed affect braking force?
Greater breaking force is required to stop a certain distance. This will cause rapid deceleration. Breaks can overheat
What is momentum?
The product of mass and velocity. All moving objects have momentum, if it is stationary, its momentum is zero
What is the formula for momentum?
Momentum = mass * velocity
(kg m/s) (kg) (m/s)
What is the conservation of momentum?
In a closed system, total momentum before an event = total momentum after an event
How do things like seatbelts and air bags protect you?
They increase the time taken for you to stop, therefore decrease the rate of change of momentum, meaning less force is applied.
What is the formula for change in momentum?
Force (N) = (mass (kg) * change in velocity (m/s) / change in time (s)
Why can rapid changes in momentum be fatal?
They result in a huge force being applied, which is dangerous. Risk can be reduced by making the change in momentum happen over a longer time
