1. Motion

What do speed, displacement, velocity + acceleration mean?

• Speed - how fast something is moving (scalar)

• Displacement - how far something has travelled with a direction (vector)

• Velocity - rate of change of displacement (vector)

• Acceleration - rate of change of velocity (vector)

How is velocity + acceleration represented on a displacement-time graph?

• Velocity → gradient

• Acceleration → how gradient changes

How is displacement + acceleration represented on a velocity-time graph?

• Displacement → area under the graph

• Acceleration → gradient

What are the five equations for constant acceleration?

• a = (v - u) / t

• s = ½ (u + v) t

• s = ut + ½ at²

• s = vt - ½ at²

• v² - u² = 2as

What are two methods of investigating motion?

• Light gates + data logger

• Video

How to do the light gate method to investigate motion?

1. Setup up a ramp + light gate at bottom

2. Measure the length of the trolley

3. Input length of trolley to data logger

4. Let go of trolley at top of the ramp

5. Data logger will calculate velocity

How to do the video method to investigate motion?

1. Setup up a ramp + put ruler on it

2. Setup video camera

3. Let go of trolley at top of the ramp

4. See how many frames it takes to pass a certain point on the ruler to calculate the velocity at that point

What are two methods of investigating the value of g in free fall?

• Electromagnet + trapdoor

• Light gates

How to do the electromagnet + trapdoor method to investigate the value of g?

1. Setup a ball bearing on a electromagnet on clamp stand, connected to a digital timer and trapdoor at the bottom

2. Measure the height from the the bottom of the ball bearing to the trapdoor

3. Flick the switch of the timer so that the ball bearing drops

4. Record reading on timer

5. Repeat 3 times + average time

6. Repeat at different heights

7. Plot graph of height (y-axis) against time² (x-axis)

8. Gradient gives you ½ g because s = ½ at²

What are two advantages of the electromagnet + trapdoor method?

• Using a small + heavy ball bearing means drag is negligible

• A digital timer is more accurate than using a stopwatch

What is the main source of error in the electromagnet + trapdoor method?

Measurement of height

How to do the light gate method to investigate the value of g?

1. Setup a clamp stand with two light gates attached to a data logger

2. Measure the height between the two light gates

3. Measure the length of an interrupt card

4. Drop the interrupt card through the light gates

5. Record velocity at each light gate

6. Repeat varying the distance between the two light gates

7. Plot graph of v² - u² (y-axis) against distance (x-axis)

8. Gradient is 2g because v² - u² = 2as

How to do projectile motion questions?

The horizontal + vertical components are independent (e.g a ball is thrown at an angle of 50° at 12 m/s → horizontal velocity is always the same but vertical velocity decreases due to gravity)

What is thinking, braking + stopping distance?

• Thinking distance - distance travelled during driver’s reaction time

• Braking distance - distance travelled from when the brakes are pressed to when the vehicle stops

• Stopping distance = thinking distance + braking distance

What two factors is thinking distance affected by?

• Initial speed

• Reaction time → affected by tiredness, alcohol + drugs

What five factors is braking distance affected by?

• Initial speed

• Mass of the vehicle

• Condition of brakes

• Condition of tyres

• Condition of road (e.g weather)

What is the formula for braking distance?

x = mv² / 2F (braking distance = mass x velocity² / 2 x force)