May the Forces be with you!April 21, 2023

On the ADMIT ONE ONLY side complete the three questions. Do you have any questions of your own from

the past few lessons? Write them down.

Name three examples of force?

What is acceleration?

What is mass?

Learning Objectives

• Explain the relationship between the resultant force (FR) on an object of mass (m) and its acceleration (a).• State and use the equation FR = ma

to determine the acceleration of an object.

maFR

2/ smkgN

m

Fa

m

ma

m

F

maF

R

R

R

m

Fa R

m

Fa R

aa

m

Fa

m

Fa

m

Fa

R

R

R

5

4

202

2010

aa

m

Fa

m

Fa

m

Fa

R

R

R

20

2

40

2

2010

Reviewing proportionalities

Experiment: what is the relationship between mass and weight?

• You and a partner are given a kilogram of slotted masses. Weigh one, then two etc. using a newton-meter and then find their mass using a balance

• Record this in the table• Plot this data on a graph using a

sharpened pencil and draw a line of best fit using a ruler.

1. What do you have to do to the mass to get the weight?

2. What is the relationship between mass and weight?

3. Can you write it as an equation?

EXTENSION:Use the equation of a straight line to

determine the gradient of the graph and include units!

What would happen if the experiment were repeated in water? In syrup?

mgW

maF

Worked example 1

• Mr Chitty is late for school. He is driving his car, which has a mass of 1500 kg, through Ilford when he stops at the traffic lights. He is getting impatient at the lights so when they turn green he puts his foot down and the engine provides a force of 20 000 N. What is the acceleration produced by the engine?

2m/s 13

1500

20000

?

1500

20000

a

kg

Na

m

Fa

maF

a

kgm

NF

Worked example 2

• The space shuttle Discovery has a mass of 25 000 kg. Astronauts would be very uncomfortable if the acceleration were above 30 m/s2. What is the force generated by the rockets?

Worked example 2

• The space shuttle Discovery has a mass of 25 000 kg. Astronauts would be very uncomfortable if the acceleration were above 30 m/s2. What is the force generated by the rockets?

NF

kgF

maF

a

kgm

F

3000000

m/s 30100000

m/s 30

100000

?

2

2

A1: Renee is cycling down the street and pedalling with a force of 150 N. She is carrying all her school books in her backback and has a total mass of 100 kg. What is her acceleration?

A2: Taran and Izzaz are helping move Ms. Wilmot’s desk in her office. It has a mass of 100 kg and they accelerate it 1 m/s2. What is their total force?

A3: Thaniya is a keen swimmer. She can push off of the wall in a turn with a force of 200 N. This gives her an acceleration of 3 m/s2. What is her mass?

G1. Sophie is skateboarding along the road. The friction from the road is 10 N. She can push the skateboard with a force of 80 N. Her mass and that of the skateboard is 70 kg. What is the acceleration?

G2. George is riding his unicycle again! The combined weight of George and his unicycle is 1000 N. He pedals with a force of 200 N but the friction between the tyre and the road is 20 N. What is his acceleration?

R1: Christine is skydiving when she should be doing her homework. Her total weight including her fancy dress costume is 1000 N. The air resistance is 30 N. What is her resultant force?

R2: Aisha and Omar are sitting in a rubber dinghy in the sea. Their combined weight is 1500 N. They are floating comfortable in the sea and therefore have no vertical acceleration. What is the resultant force on them?

G3. Isabella is driving a motorbike through the canteen with an acceleration of 20 m/s2. Isabella and the bike have a mass of 800 kg. There is a frictional force of 50 N on each wheel. What is the force from the engine?

R3: Mihrab and Jaswinder are playing cricket. Jaswinder bowls the 0.2 kg ball at Mihrab who hits it for 6. What is the weight of the ball?

A1: Renee is cycling down the street and pedalling with a force of 150 N. She is carrying all her school books in her backback and has a total mass of 100 kg. What is her acceleration?

A2: Taran and Izzaz are helping move Ms. Wilmot’s desk in her office. It has a mass of 100 kg and they accelerate it 1 m/s2. What is their total force?

A3: Thaniya is a keen swimmer. She can push off of the wall in a turn with a force of 200 N. This gives her an acceleration of 3 m/s2. What is her mass?

G1. Sophie is skateboarding along the road. The friction from the road is 10 N. She can push the skateboard with a force of 80 N. Her mass and that of the skateboard is 70 kg. What is the acceleration?

G2. George is riding his unicycle again! The combined weight of George and his unicycle is 1000 N. He pedals with a force of 200 N but the friction between the tyre and the road is 20 N. What is his acceleration?

R1: Christine is skydiving when she should be doing her homework. Her total weight including her fancy dress costume is 1000 N. The air resistance is 30 N. What is her resultant force?

R2: Aisha and Omar are sitting in a rubber dinghy in the sea. Their combined weight is 1500 N. They are floating comfortable in the sea and therefore have no vertical acceleration. What is the resultant force on them?

G3. Isabella is driving a motorbike through the canteen with an acceleration of 20 m/s2. Isabella and the bike have a mass of 800 kg. There is a frictional force of 50 N on each wheel. What is the force from the engine?

R3: Mihrab and Jaswinder are playing cricket. Jaswinder bowls the 0.2 kg ball at Mihrab who hits it for 6. What is the weight of the ball?

A1: 1.5 m/s2

A2: 100 N

A3: 67 kg

G1. 1 m/s2

G2. 1.8 m/s2

R1: 970 N

R2: 0 N

G3. 16100 NR3: 2 N

Learning Objectives

• Explain the relationship between the resultant force (FR) on an object of mass (m) and its acceleration (a).• State and use the equation FR = ma

to determine the acceleration of an object.

Nam

e three examples of force?

What is acceleration?

What is m

ass?

Nam

e three examples of force?

What is acceleration?

What is m

ass?

Nam

e three examples of force?

What is acceleration?

What is m

ass?

Nam

e three examples of force?

What is acceleration?

What is m

ass?

1.

2.3. 1.

2.3. 1.

2.3. 1.

2.3.