Book 2: Force and Motion Flashcards
What are the SI units of length and time?
length: metre (m)/kilometre (km), centimetre (cm), millimetre (mm)
time: second (s)/microsecond (μs), millisecond (ms)
What is the average reaction time of a person?
0.2s
How can we overcome the limits of reaction time?
We can measure the duration of repeating events for more cycles or use automatic devices like light-gates connected to a timer-scaler or data-logger.
What is displacement and what type of measurement is it?
Displacement is the change in position relative to the starting position, and it requires both magnitude (size) and direction. Therefore, it is a vector.
What is the difference between vectors and scalars?
Vectors require both magnitude and direction, but scalars only require magnitude.
How can the total displacement be calculated?
If the displacement is along a straight line, the total displacement has the magnitude and direction of the arrow pointing from the starting point to the finishing point. If the displacement is along a plane, Pythagoras’ theorem and trigonometry can be used to find its magnitude and direction.
What is speed and what is its unit? Is it a vector or scalar?
Speed is the distance travelled per unit time, measured in an SI unit of ms^-1 (m/s). It is a scalar because it does not require direction.
What are average speed and instantaneous speed?
Average speed measures how fast an object moves over a whole journey. It is obtained by dividing the total distance travelled by the time taken. Instantaneous speed is the average speed over an extremely short time; the shorter the time period, the more accurate the measurement.
What is velocity and what is its unit? Is it a vector or scalar?
Velocity is the displacement per unit time, measured in an SI unit of ms^-1. It is a vector because it has both magnitude and direction.
What are average velocity and instantaneous velocity?
Average velocity measures the displacement of an object over a whole journey. It is obtained by dividing the total displacement travelled by the time taken. It may not be equal to the average speed. Instantaneous velocity is the average displacement over an extremely short time; the shorter the time period, the more accurate the measurement. Its magnitude is always equal to that of instantaneous speed.
What does it mean when an object is in uniform motion?
It is moving in constant velocity, which means it is moving at a constant speed in a fixed direction.
What is acceleration and what is its unit? Is it a vector or scalar?
Acceleration is the change in velocity per unit time, measured in an SI unit of ms^-2. It is a vector because an object has acceleration when its direction changes as well.
What is average acceleration?
Average acceleration is the total change of velocity in the total time travelled.
How can we tell whether an object is speeding up or slowing down from its velocity and acceleration?
If the velocity and acceleration have the same sign, the object is speeding up. If they have opposite signs, then the object is slowing down. We cannot tell the direction or acceleration of an object from only the sign of its velocity, or only the sign of its acceleration.
What is a s-t graph and what are its features?
An s-t graph is a displacement-time graph, with the displacement being plotted on the y-axis against the time. Its slope give the velocity of the object.
What is a v-t graph and what are its features?
A v-t graph is a velocity-time graph, with the velocity being plotted on the y-axis against the time. The slope of a v-t graph gives the acceleration of an object. When the graph is a straight line or curve, the sign of the slope gives the direction of acceleration and the steeper the slope, the greater the magitude of acceleration. The area under a v-t graph is the total displacement of the object.
What is an a-t graph?
An a-t graph is an acceleration-time graph, with the acceleration being plotted on the y-axis against the x-axis.
What are the looks of the s-t, v-t, and a-t graphs when an object is in uniform motion?
The s-t graph is a straight line, the v-t graph is a horizontal line (y=v, where v is the constant velocity), and the a-t graph is a horizontal line (y=0)
What are the looks of the s-t, v-t, and a-t graphs when an object is uniformly accelerated?
The s-t graph is a curved line curved upwards, the v-t graph is a straight line with a slope, and the a-t graph is a horizontal line (y=a, where a is the constant acceleration)
What are the looks of the s-t, v-t, and a-t graphs when an object is uniformly accelerating with direction opposite to its velocity?
The s-t graph is a downward-opening parabola, the v-t graph is a straight line with slope from positive to negative, and the acceleration is a horizontal line (y=a, where a is the constant acceleration and a<0)
What are the equations of uniformly accelerated motion?
v=u+at, s=1/2(v+u)t=ut+1/2at^2, v^2=u^2+2as
Why do objects fall at different speeds?
Objects fall due to gravity, and they fall at different speeds because of air resistance. If air is removed, objects fall at the same rate.
What is the acceleration due to gravity?
9.81 ms^-2 near the earth’s surface and pointing downwards, denoted by g
What is a force and its unit? Is it a vector or scalar?
Force is a push or pull on an object by another object, and it exists in pairs. Its SI unit is newton (N), and it is a vector because it has both magnitude and direction.