Chapter 2: Motion In A Straight Line

Question 1

Accelerating motion

Answer 1

Movement involving changes in speed or direction or both

Question 2

Non-accelerating motion

Answer 2

Movement in a straight line at a constant speed

Question 3

Displacement

Answer 3

• The shortest distance from one point to another, in a certain direction
• The change of position of an object in a given direction
• A vector quantity

Question 4

Distance

Answer 4

• The amount of ground covered
• How far you have travelled
• The path taken, or travelled
• Scalar quantity

Question 5

Speed

Answer 5

• Scalar quantity
• Defined as the rate of change of distance
• Average speed = total distance / total time
• Instantaneous speed = small distance travelled in a stated direction / time taken for this small distance

Question 6

Velocity

Answer 6

• Speed in a particular direction
• The rate of change of displacement
• Vector quantity
• Average velocity = total displacement / total time
• Instantaneous velocity = small displacement travelled in a stated direction / time take for this small displacement

Question 7

Residual error

Answer 7

|average - furthest away data|

Question 8

Kinematics

Answer 8

The study of motion

Question 9

Acceleration

Answer 9

• Rate of change of velocity
• Slope of a velocity-time graph gives acceleration

a = final velocity - initial velocity / time taken

Question 10

Velocity-time graph

Answer 10

• Slope gives acceleration
• Area beneath gives displacement
• Straight line sloping upwards indicates constant acceleration
• Straight line sloping downwards indicates constant deceleration
• Horizontal line indicates zero acceleration, that is, constant velocity

Question 11

Acceleration-Time graph

Answer 11

• Area beneath gives velocity
• Horizontal line on x-axis indicates zero acceleration, so constant velocity
• Horizontal line otherwise indicates constant acceleration

Question 12

Acceleration due to gravity

Answer 12

• Galileo first proved that, if we ignore the effect of air resistance, the acceleration of falling objects is constant, and doesn’t depend on mass
• Acceleration due to gravity = 9.8 m/s/s down
• When air resistance is assumed to be negligible, we say the objects is ‘free falling’

Question 13

Two main forms of motion due to gravity

Answer 13

Vertical motion - object moves in one dimension only, that is, up and down
Projectile motion - object moves horizontally as well as vertically (e.g. stone thrown off cliff)

Question 14

Types of free-fall motion

Answer 14

1. Object is being dropped or thrown down
2. Object is being thrown upward

• Up direction is positive acceleration, therefore acceleration due to gravity is constant at 10 m/s/s in the negative direction
• Negative acceleration does not always mean deceleration
• If an object is moving in the negative direction and has negative acceleration then it will get faster in that negative direction
• If it is moving in the positive direction and has a negative acceleration then it is slowing down in that positive direction

Question 15

Case 1 of free-fall motion: Dropped or thrown down

Answer 15

• In both cases velocity increases
• When dropped, initial velocity is zero, but when thrown down the velocity begins at some negative value
• Either way, velocity begins at some negative value

Question 16

Case 2 of free-fall motion: Throwing an object upward

Answer 16

• Object starts at a high initial velocity in the positive direction
• Gradually slows to a halt at the top of its flight (v = 0)
• Gradually increases velocity in the negative direction until it returns to the ground
• Time of flight up equals time of flight down
• Acceleration is constant even at the top of flight when v=0
• Initial speed equals final speed
• Final velocity equals negative of initial velocity

Question 17

Ticker timer

Answer 17

• Records the motion of an object
• Specifically designed for physics experiments
• Has a metal arm that vibrates at constant intervals (up and down 50 times per second)
• A needle on the arm strikes carbon paper and records dots on paper tape pulled through the timer
• The dots give a record of motion (distance between can be used to calculate the velocity of the moving object)
• The faster the motion, the greater the space between dots

Question 18

Displacement-time graphs

Answer 18

• Slope of the line gives velocity
• If the graph goes up in a straight line the velocity is constant
• If the function is a curve, then a tangent must be drawn to find instantaneous velocity
• Horizontal line indicates no movement
• If line curves upwards, this indicates constant acceleration