Motion and Forces Flashcards
Define Acceleration
Rate of the change in velocity
Equation for acceleration
Acceleration= change in velocity divided by the time taken
Change in velocity is
Final velocity-initial velocity
What is Newton’s first law?
When there is no resultant force an object that is stationary will remain stationary and an object in motion will continue in a straight line at constant speed.
What is needed for acceleration?
Force/ a resultant force
What does Newton’s Second Law say?
Resultant force = mass x acceleration
f=ma
What two things make up stopping distance?
Thinking distance+ braking distance
What factor affects both thinking and braking distance?
Speed
Factors affecting thinking distance (generally about the person).
Alcohol. Tiredness. Age. Distractions.
Factors affecting braking distance (about vehicle and road).
Road surface. Weight of car. Quality of brakes. Slope.
Why does the box and parachute fall at a terminal/constant velocity?
Drag acts upwards, weight acts downwards. Drag and weight are balanced. Constant velocity means no acceleration (f=ma). When forces are balanced there is no acceleration.
Why are arrows good for representing vector quantities?
Can show both size and direction. Can show where they act from/ their origin.
Weight equals?
Mass x gravitational field strength
Resultant force equals?
Mass x acceleration
Step 1 of terminal velocity (skydiver has just jumped out of airplane)
Object accelerates due to resultant force downwards. Weight, acting downwards, is only force acting vertically at the moment.
Step 2 of terminal velocity (skydiver is falling, still no parachute)
As object accelerates, speed and drag increase. Therefore, resultant force decreases and acceleration decreases .
Step 3 of terminal velocity (skydiver reaches terminal velocity)
Eventually, drag equals weight. There is no resultant force and no acceleration. Object moves at constant speed- object has reached terminal velocity.
Step 4 of terminal velocity (skydiver opens parachute)
Drag increases. Drag is greater than weight. Resultant force is upwards. Skydiver decelerates.
Step 5 of terminal velocity (terminal velocity again)
Drag is reduced. Forces are balanced. Resultant force is zero. This terminal velocity is not as fast as previous terminal velocity.
What is the difference between weight and mass?
Weight is the pull of a planet’s gravitational force acting on an object. Measured in Newtons. Weight can change depending on the planet’s gravitational field strength.
Mass is the amount of matter inside and object. Measured in kilograms. Mass stays the same.
Light Gates
Object passes through gate and breaks a light beam. When beam of light is broken, timer is started. When beam is no longer broken, timer stops. Speed = length of object/ time beam broken.
Stopwatch and ruler
Measure distance travelled (using ruler).
Timer how long it takes for object to travel distance (use stopwatch). Speed= distance/time
Motion Sensor
Uses echolocation.
Sends out a sound pulse and starts a timer.
When sound pulse reflects off a surface and returns, the pulse is detected and the timer stops.
Distance= speed of sound x time taken to return.
Speed can then be calculated.
What is Newton’s 1st Law?
Newton’s 1st Law says that the velocity of an object will only change if a resultant force is acting on the object. This applies to a stationary (still) or moving object. If an object is moving and there is no resultant force acting on it, the object will continue moving in the same direction at the same speed.
This means that the object will continue moving at the same velocity.
This also means that the velocity of an object will only change if a resultant force is acting on the object.
Thinking distance
Distance travelled from when driver realises they need to brake to when they apply brakes.
Braking distance
Distance car travels between the driver applying the brakes and the car stopping.
Describe how you could measure the average speed of a cyclist going round a track.
- Mark start and finish line.
- Measure distance of one lap around the track using a trundle wheel.
- Time how long it takes for cyclist to complete one lap of the track using a stopwatch.
- Repeat and find an average.
- Find speed using speed = distance over time.
What happens to thinking distance when speed doubles?
Thinking distance also doubles.
What happens to braking distance when speed doubles?
Braking distance quadruples.
