Motion Flashcards
Scalar quantity
A quantity with magnitude but no direction
Vector quantity
A quantity with magnitude and direction
Speed
Rate of change of distance travelled
Average speed
Total distance travelled divided by the time taken
How could you use standard laboratory equipment to determine the average speed at which a marble rolls down a slope? Include quantities which you measure and equipment used.
1) measure the distance the marble travels between two marked points using a meter ruler / tape measure
2) measure the time take for the marble to travel between two marked points using a stopwatch
3) using speed= distance/time calculate the average speed of the marble
Suggest why your value may differ from that of a value obtained using a radar speed trap.
-Zero error: not starting watch at 0
-delay in reaction time for starting and stopping watch
-measurement error (parallax) on time measurement
Hoe can you use light gates to measure average speed over a fixed distance?
1) connect two light gates to an electronic timer. When the object passes through the first light gate, the timer will start. When the object passes through the second gate the timer will stop.
2) measure the distance that the object has travelled between the two light gates using a meter ruler.
3) using speed = distance/time, calculate the average speed of the object
Displacement
Distance moved in a stated direction (in a straight line)
Velocity
Rate of change of displacement
Acceleration
Rate of change of velocity
Explain how Galileo disproved the idea that “heavier objects fall faster than lighter ones”.
two cannonballs of different mass (but same size) are dropped from the same height at the same time.
They hit the ground at the same time so both have the same acceleration
Describe an experiment to estimate the acceleration g of free fall. Include:
-measurements taken/equipment used
-how the measurements are used to estimate g
-an explanation of why the value g is an estimate
1) measurements taken/equipment used:
-measure the distance the ball falls using a meter ruler (or tape measure)
-measure the time the ball is falling for using a stopwatch
2)how the measurements are used to estimate g
-s= ut+ 1/2at^2 and u=0m/s and so s=1/2at^2
-Plot a graph of s vs t^2, and g=2* gradient
3) an explanation why the value of g is an estimate:
- drag (air resistance) acting on the ball is ignored
-There is a reaction time on starting and stopping the stopwatch
-Parallax errors with the time at which the ball hits the ground are not accounted for
What is the thinking distance?
Distance travelled from when the driver sees a problem and the brakes are applied.
What is the braking distance?
Distance travelled from when the driver starts braking to when the car stops
What is the stopping distance?
Distance travelled from when the driver sees a problem to when the car stops
(Thinking distance + braking distance)
Describe and explain factors that increase the braking distance of a car.
1) A greater speed: braking distance is directly proportional to the speed squared.
2) A greater mass: braking distance is directly proportional to the mass
3) Worn tyres/brakes: friction acting between the car and the road increases
4) wet / slippery/ icy roads roads: friction acting between the car and road decreases
5) A downhill slope: the component of acceleration parallel to the slope increases
Describe the factors that increases the thinking distance of a car.
1) consumption of drugs/alcohol
2) driver fatigue / distractions
3) A greater speed: a greater distance is travelled during the reaction time
How does braking distance depend on the speed and mass of the vehicle?
-Braking distance is directly proportional to speed^2
-braking distance is directly proportional to the mass
Define acceleration
Rate of change of velocity
When solving projectile motion problems on Earth, what assumption is made regarding acceleration?
1) air resistance is not taken into account.
2) vertical component of acceleration = -9.81ms^-2.
3) horizontal component of acceleration = 0ms^-2
Define instantaneous speed.
The speed at a particular time
How does thinking distance depend on the speed of the vehicle?
Thinking distance is directly proportional to the speed
For a projectile, how do you calculate the time of flight of the object?
1) calculate the time taken for the object to reach maximum height (vertical component of velocity=0)
2) multiply the answer by 2.
For a projectile, how do you calculate the time of flight of the object?
1) calculate the time taken for the object to reach maximum height (vertical component of velocity = 0)
2) multiply the answer by 2.
What does the gradient of a velocity-time graph represent?
Acceleration
How do you calculate the stopping distance?
Stopping distance = thinking distance + braking distance
