Y2_T4_LSN_4.3

• Science
• Middelbare school
• havo, vwo
• Leerjaar 2

Get ready

• Your Macbook (join the LessonUp)
• Your notebook.
• Your textbook.
• Pen & highlighter

Topic 4

Moving in the world

Plan for today

• Explanation T4.3 Acceleration
  
• Make homework
  

4.3 Acceleration

Learning goals

I can....

• describe the concept of acceleration and understand which measurements and units are necessary to calculate it.
• calculate the acceleration of an object using the acceleration formula.
• create and interpret v,t-diagrams relating to an object’s change in motion.
• use an object’s resultant force to determine what type of motion it has.

Key words

• Acceleration
• Deceleration
• v,t-diagram

Acceleration

Acceleration is change in speed, so speeding up or slowing down, measured in meters per second squared 

m/s​2​​

Deceleration

Acceleration is an increase in speed

a is a positive number.

A decrease in speed is called decelaration

a is a negative number

Acceleration example

Acceleration is positive when speed increases

If the speed increases by 20 m/s in 5 seconds

delta v = v(final) - v(initial)

delta v = 20 - 0 = 20 m/s (so it is positive)

a = 20/5 = 4               (also positive)

m/s​2​​

Deceleration example

Acceleration is negative (= deceleration) when speed decreases

If the speed decreases by 20 m/s in 5 seconds

delta v = v(final) - v(initial)

delta v = 0 - 20 = -20 m/s (so it is negative)

a = -20/5 =  -4               (also negative)

m/s​2​​

Petra is at a traffic light. As soon as it hits green, she starts to speed up on her bike. She accelerates with 5
What is her speed after 4 seconds?

m/s​2​​

1. 9 m/s
2. 1 m/s
3. 20 m/s
4. 1,25 m/s

A car is accelerating for 8 seconds, increasing by 20 m/s every second. What is his final speed?

1. 28 m/s
2. 160 m/s
3. 2,5 m/s
4. 12 m/s

convert 18 m/s to km/h

1. 14,4 km/h
2. 65 km/h
3. 5 km/h
4. 21,6 km/h

v,t-diagram

An v,t -Diagram is a graph that shows the speed of an object.

it shows the speed (v) and the time (t)

s,t-diagram vs v,t-diagram

Moving at a constant speed gives me these 2 graphs

Notice that the first is an s,t-diagram,

The second one is a v,t-diagram

s,t-diagram vs v,t-diagram

Moving at a constant acceleration gives me these 2 graphs

Notice that the first is an s,t-diagram,

The second one is a v,t-diagram

s,t-diagram vs v,t-diagram

Moving at a constant negative acceleration gives me these 2 graphs

Notice that the first is an s,t-diagram,

The second one is a v,t-diagram

Calculating forces (4.1)

Forces (no acceleration)

If the resultant force is 0 N, the object is not accelerating

The speed is constant

standing still is also a constant speed (0 m/s)

Forces (acceleration)

If the resultant force is + N, the object will accelerate

(+ means it is in the same direction as the movement)

Forces (deceleration)

If the resultant force is - N, the object will decelerate

(- means the resultant force is opposite to the direction of movement)

What kind of movement will happen in this situation?

1. constant speed to the left
2. constant speed to the right
3. acceleration to the left
4. acceleration to the right

What kind of movement wil happen here

1. constant speed downwards
2. constant speed upwards
3. deceleration downwards
4. deceleration upwards

On an object the following forces are acting:
50 N to the right
20 N upwards
75 N to the left
20 N downwards
What type of motion will happen?

1. acceleration upwards
2. acceleration to the right
3. acceleration downwards
4. acceleration to the left

Homework

• Study the glossary of 4.3
  
• Complete the exercises of 4.3 (p. 176-181)

Next lesson = homework check (4.1, 4.2 & 4.3) 

+ Practice test