Do now! Homework Due Weds 10th Feb Complete trolley AND balls investigation

Last lesson

No movement distance time speed time

Constant speed distance time speed time Area = distance travelled

Constant acceleration distance time speed time Area = distance travelled

Today’s lesson Newton’s Laws of Motion That’s me!

Newton’s 1 st law Newton’s first law was actually discovered by Galileo. Newton nicked it!

Newton’s 1 st Law If there is no resultant force acting on an object it will be stationary or move with constant velocity.

Newton’s 1 st Law If there is no resultant force acting on an object it will be stationary or move with constant velocity. Does this make sense?

Newton’s first law Imagine a marble rolling in a very smooth (i.e. no friction) bowl.

Newton’s first law If you let go of the ball, it always rolls up the opposite side until it reaches its original height (this actually comes from the conservation of energy).

Newton’s first law No matter how long the bowl, this always happens

Newton’s first law No matter how long the bowl, this always happens. constant velocity

Newton’s first law Imagine an infinitely long bowl where the ball never reaches the other side!

Newton’s first law The ball travels with constant velocity until its reaches the other side (which it never does!). Galileo realised that this was the natural state of objects when no (resultant ) forces act. constant velocity

Another example Imagine Mr Porter cycling at constant velocity.

Newton’s 1 st law He is providing a pushing force. Constant velocity

Newton’s 1 st law There is an equal and opposite friction force. Constant velocity Pushing force friction

Another example - Falling!

Imagine a dog being thrown out of an aeroplane. Woof! (help!)

Force of gravity means the dog accelerates gravity To start, the dog is falling slowly (it has not had time to speed up). There is really only one force acting on the dog, the force of gravity. The dog falls faster (accelerates) due to this force.

Gravity is still bigger than air resistance gravity As the dog falls faster, another force becomes bigger – air resistance. The force of gravity on the dog of course stays the same The force of gravity is still bigger than the air resistance, so the dog continues to accelerate (get faster) Air resistance

Gravity = air resistance Terminal speed gravity As the dog falls faster and air resistance increases, eventually the air resistance becomes as big as (equal to) the force of gravity. The dog stops getting faster (accelerating) and falls at constant velocity. This velocity is called the terminal velocity. Air resistance

Terminal Speed The dog will continue to fall at constant speed (called the terminal speed) until…………. gravity Air resistance air resistance = gravity

Terminal Speed gravity Air resistance

Oooooops!

That definitely was terminal! YouTube - Concept Physics 03 - Newton's First Law

Newton’s first law Can you draw four examples of objects moving with constant velocity. Show (by using arrows) and label the forces on the objects.

Newton’s second law Newton’s second law concerns examples where there is a resultant force. I thought of this law myself!

Let’s go back to Mr Porter on his bike. Remember when the forces are balanced (no resultant force) he travels at constant velocity. Constant velocity Pushing force friction

Newton’s 2nd law Now lets imagine what happens if he pedals faster. Pushing force friction

Newton’s 2nd law His velocity changes (goes faster). He accelerates! Pushing force friction acceleration

Newton’s 2nd law Now imagine what happens if he stops pedaling. friction

Newton’s 2nd law He slows down (decellerates). This is a negative acceleration. friction

Newton’s 2nd law So when there is a resultant force, an object accelerates (changes velocity) Pushing force friction Mr Porter’s Porche

Falling without air resistance Oh no! He’s going to kill another dog!

Falling without air resistance

gravity This time there is only one force acting in the ball - gravity

Falling without air resistance gravity The ball falls faster….

Falling without air resistance gravity The ball falls faster and faster…….

Falling without air resistance gravity The ball falls faster and faster and faster……. It gets faster by 10 m/s every second (10 m/s 2 ) This number is called “g”, the acceleration due to gravity.

Newton’s 2 nd law There is a mathematical relationship between the resultant force and acceleration. Resultant force (N) = mass (kg) x acceleration (m/s 2 ) F R = ma It’s physics, there’s always a mathematical relationship!

Newton’s 2 nd law There is a mathematical relationship between the resultant force and acceleration. Resultant force (N) = mass (kg) x acceleration (m/s 2 ) F R = ma Don’t sweat, you’ll learn to use this next year!

Newton’s second law Can you draw four examples of objects moving with constant acceleration. Show (by using arrows) and label the forces on the objects.

Newton’s 3 rd law If a body A exerts a force on body B, body B will exert an equal but opposite force on body A. Hand (body A) exerts force on table (body B) Table (body B) exerts force on hand (body A)

Don’t worry! We won’t do Newton’s 3 rd law until year 12! YouTube - Three Laws of Motion

That’s all folks!

Let’s try some writing some questions! Page 146 & 147 Can you write 6 multiple choice questions of your own to go with these pages?