1. Force diagrams… The block has 2 opposing forces being applied to it:
7N to the right and 4N to the left.
They are Unbalanced Forces…
To Calculate the Resultant Force (∑F) acting on the block,
subtract one from the other: 7N – 4N = 3N to the right 3N

2. Application of Forces ∑F=0 ∑F=ma Balanced forces (1st Law)
When opposing forces are equal
E.g. when an object is not moving or when an object is moving at a constant speed
Unbalanced forces (2nd Law)
When opposing forces are unequal
E.g. when an object accelerates
∑F=0
∑F=ma

3. Are the forces acting on a car that is travelling at a constant speed, balanced or unbalanced?
Newton's
1st Law
∑F=0

4. Are the forces acting on a car that is slowing down, balanced or unbalanced?
Newton's 2nd Law
∑F=ma

5. Are the forces acting on a car that is not moving, balanced or unbalanced?
Newton's 1st Law

6. Newton's
1st Law or
2nd Law ?

8. Friction Friction happens when two objects or surfaces touch
Friction tries to stop or slow things down
Friction acts in the opposite direction to the movement.
Friction
Thrust

9. Heat energy is always produced.
Friction is a force. It occurs when two surfaces rub together.
Heat energy is always produced.

10. Ice on wooden bench Wood on wooden bench Add a lubricant such as oil

12. ∑F=ma
∑F=0
∑F=ma

13. Friction can be useful:
friction between our shoes and the floor stop us from slipping
friction between tyres and the road stop cars from skidding
friction between the brakes and wheel help bikes and cars slow down
Frictional forces are much smaller on smooth surfaces than on rough surfaces, which is why we slide on ice.

14. Unhelpful frictional forces
If you don't lubricate your bike regularly with oil, the friction in the chain and axles increases. Your bike will be noisy and difficult to pedal.
When there is a lot of friction between moving parts, energy is lost to the surroundings as heat.

15. Friction helps you build a house of cards.
FACT OR FRICTION
Which of the following are fact (true) and which are fiction (false)?
Friction helps you build a house of cards.
Friction explains how you can whip a tablecloth off a fully laid table without breaking anything.
Friction makes electrical equipment heat up.
The pattern on tyres causes friction with the road. This helps to control the vehicle.
People use friction to start fires.
Friction helps skiers to ski up hill.
Runners use friction to run without slipping.
Friction causes people to get burnt by snow.
Answers: 1 Fact; 2 Fiction; 3 Fact; 4 Fiction (smooth tyres provide more friction in dry weather. The treads are better in wet weather as the wheel scoops the water out of the way so the tyres can grip the road); 5 Fact; 6 Fact; 7 Fact; 8 Fact (at high speeds, friction causes enough heat to burn the skin before the snow melts)

16. Air resistance
Bikes, cars and other vehicles experience air resistance as they move.
Air resistance is caused by the frictional forces of the air against the vehicle.
The faster the vehicle moves, the bigger the air resistance becomes.
How do racing cyclists reduce the air resistance on them?
crouch down low on their bikes
wear streamlined helmets (special, smooth shapes that allow the air to flow over the cyclist more easily)
shave their legs

18. Weight force due to Gravity
Gravity is a force that pulls objects downwards towards the centre of the earth.
Gravity is the force that gives us weight

19. Mass and Weight
The mass (kg) of an object is the amount of matter that is in the object
the weight (N) of an object is the force of gravity that acts on that object
Mass is related to how much ‘stuff’ is there and weight is related to the ‘pull’ of the Earth

20. Ethel may be happy about her diet, but her science isn’t so great!
I’m sorry! I should have said that my MASS has gone down from 70kg to 68kg.
Great! I have lost another 2 kilograms. My weight has gone down from 70kg to 68kg.
68.0 kg
Ethel may be happy about her diet, but her science isn’t so great!
Tell Ethel what she should have said instead.

21. This object has a ……………. of 2……. This object has a ……………. of …….
2.00 kg
1.30 kg
This object has a ……………. of 2…….
This object has a ……………. of …….
mass
mass
1.3kg kg
The same object has a ……………. of 20 …….
The same object has a ……………. of …….
weight
weight N
13N 10
On Earth an object’s weight is always ……… times bigger than its mass

22. The Four Forces of Flight
The Four Forces of Flight Keep This Plane AloftHave you ever thrown a Frisbee®? It flies because of four forces. These same four forces help an airplane fly. The four forces are lift, thrust, drag, and weight. As a Frisbee flies through the air, lift holds it up. You gave the Frisbee thrust with your arm. Drag from the air made the Frisbee slow down. Its weight brings the Frisbee back to Earth again.
You see them everyday: airplanes, jets, and helicopters, soaring, zooming, and even roaring through the skies. We may take flight for granted; yet, knowing the science behind it gives us a better understanding of the marvels of air travel.
Wings keep an airplane up in the air, but the four forces are what make this happen. They push a plane up, down, forward, or slow it down.
     
* Thrust is a force that moves an aircraft in the direction of the motion. It is created with a propeller, jet engine, or rocket. Air is pulled in and then pushed out in an opposite direction. One example is a household fan.
* Drag is the force that acts opposite to the direction of motion. It tends to slow an object. Drag is caused by friction and differences in air pressure. An example is putting your hand out of a moving car window and feeling it pull back.
* Weight is the force caused by gravity.
* Lift is the force that holds an airplane in the air. The wings create most of the lift used by airplanes.
The way the four forces act on the airplane make the plane do different things. Each force has an opposite force that works against it. Lift works opposite of weight. Thrust works opposite of drag. When the forces are balanced, a plane flies in a level direction. The plane goes up if the forces of lift and thrust are more than gravity and drag. If gravity and drag are bigger than lift and thrust, the plane goes down. Just as drag holds something back as a response to wind flow, lift pushes something up. The air pressure is higher on the bottom side of a wing, so it is pushed upward.

23. Thrust
Thrust is a force that moves an aircraft in the direction of the motion.
It is created with a propeller, jet engine, or rocket.
Air is pulled in and then pushed out in an opposite direction.
One example is a household fan.
The Four Forces of Flight
The Four Forces of Flight Keep This Plane AloftHave you ever thrown a Frisbee®? It flies because of four forces. These same four forces help an airplane fly. The four forces are lift, thrust, drag, and weight. As a Frisbee flies through the air, lift holds it up. You gave the Frisbee thrust with your arm. Drag from the air made the Frisbee slow down. Its weight brings the Frisbee back to Earth again.
You see them everyday: airplanes, jets, and helicopters, soaring, zooming, and even roaring through the skies. We may take flight for granted; yet, knowing the science behind it gives us a better understanding of the marvels of air travel.
Wings keep an airplane up in the air, but the four forces are what make this happen. They push a plane up, down, forward, or slow it down.
     
* Thrust is a force that moves an aircraft in the direction of the motion. It is created with a propeller, jet engine, or rocket. Air is pulled in and then pushed out in an opposite direction. One example is a household fan.
* Drag is the force that acts opposite to the direction of motion. It tends to slow an object. Drag is caused by friction and differences in air pressure. An example is putting your hand out of a moving car window and feeling it pull back.
* Weight is the force caused by gravity.
* Lift is the force that holds an airplane in the air. The wings create most of the lift used by airplanes.
The way the four forces act on the airplane make the plane do different things. Each force has an opposite force that works against it. Lift works opposite of weight. Thrust works opposite of drag. When the forces are balanced, a plane flies in a level direction. The plane goes up if the forces of lift and thrust are more than gravity and drag. If gravity and drag are bigger than lift and thrust, the plane goes down. Just as drag holds something back as a response to wind flow, lift pushes something up. The air pressure is higher on the bottom side of a wing, so it is pushed upward.

24. Drag (Air resistance)
Drag is the force that acts opposite to the direction of motion.
It tends to slow an object.
Drag is caused by friction and differences in air pressure.
An example is putting your hand out of a moving car window and feeling it pull back. *
     
* Weight is the force caused by gravity.
* Lift is the force that holds an airplane in the air. The wings create most of the lift used by airplanes.
The way the four forces act on the airplane make the plane do different things. Each force has an opposite force that works against it. Lift works opposite of weight. Thrust works opposite of drag. When the forces are balanced, a plane flies in a level direction. The plane goes up if the forces of lift and thrust are more than gravity and drag. If gravity and drag are bigger than lift and thrust, the plane goes down. Just as drag holds something back as a response to wind flow, lift pushes something up. The air pressure is higher on the bottom side of a wing, so it is pushed upward.

25. Weight Weight is the force caused by gravity. *
     
* Weight is the force caused by gravity.
* Lift is the force that holds an airplane in the air. The wings create most of the lift used by airplanes.
The way the four forces act on the airplane make the plane do different things. Each force has an opposite force that works against it. Lift works opposite of weight. Thrust works opposite of drag. When the forces are balanced, a plane flies in a level direction. The plane goes up if the forces of lift and thrust are more than gravity and drag. If gravity and drag are bigger than lift and thrust, the plane goes down. Just as drag holds something back as a response to wind flow, lift pushes something up. The air pressure is higher on the bottom side of a wing, so it is pushed upward.