FRICTION

Learning Outcome: Explain how the type of surface affects friction Explain how forces affect the motion of an object

Starter:Can you think of a situation where……..1)There is lots of friction2)There is only a little friction3)Where friction can be useful4)Where friction is not useful

05/03/23

Wednesday 3 May 2023

Wednesday 3 May 2023

Friction always tries to slow moving objects down – it opposes motion. Frictional forces occur when two touching surfaces move past each other, in this case the box moving across the ground.

FRICTION AND MOTION

Friction also occurs when things move through air. This is called air resistance.

pull of rope on boxfriction

Label all sources of friction acting on this bike.

WHAT ARE THE SOURCES OF FRICTION?

pedalbearing

links inchain

tyre androad

airresistance

brake pad

wheelbearing

FRICTION EXPERIMENT

Friction is a very important force for the movement of cars. It acts in the opposite direction to the movement of the car.

CARS STOPPING

The time it takes for a car to brake is affected by the frictional forces between the car’s tyres and the road surface.

thrust from engine friction

EFFECTS OF FRICTIONAL FORCES

HOW DOES A PLANE TAKE-OFF?

What forces are acting on the fish?

FORCES IN WATER

Upthrust is a force that pushes objects upwards in a liquid or a gas. This balances the weight of the fish, and is also known as buoyancy.

In order to move forward, the fish uses its tail to produce thrust. This force drives it through the water and is always opposed by friction.

thrust friction

weight

upthrust

REPRESENTING FORCES

A force is a vector quantity. It always has a size (magnitude) and

direction. We represent the force using an arrow

the length of the arrow represents the size of the force

the direction of the arrow represents the direction of the force.

TUG OF WAR

Objects can have more than one force acting on them

These forces can act in different directions The forces can be balanced or unbalanced

WHAT COULD A CAR BE DOING?

1) Accelerating2) Decelerating3) Constant speed4) Stationary

States of motion

BALANCED AND UNBALANCED FORCES –

and the object is stationary, it will remain stationary and the object is moving, it will continue to move at

the same speed and in a straight line.

If the forces are unbalanced, two things can happen:

If the forces on an object are balanced:

In other words, the object will continue to do what it is already doing without any change.

The speed can change - This is called acceleration or decceleration. The direction of motion can change.

Accelerating

Constant speed

Decelerating

IN WHAT OTHER STATE OF MOTION WOULD THE FORCES BE BALANCED?

The resultant force is calculated by working out the difference between opposing forces in each direction.What is the resultant force on this truck?

The sum effect of more than one force is called the resultant force.

A resultant force of 100 N is accelerating the truck.

RESULTANT FORCE

500 N400 N

FORCE PAIRS

500 N 500 N

Imagine a car travelling at a constant speed of 50 km/h.

BALANCED AND UNBALANCED FORCES

The engine provides sufficient force to balance all the frictional forces that are acting to decrease the speed.

20 N

1. What is the resultant force on the satellite?

Resultant force = 20 N – 10 N= 10 N down

The satellite will accelerate downwards.

RESULTANT FORCES – QUESTION 1

5 N 5 N

5 N

2. What is the resultant force on the bird?

5 N 5 N

The forces acting in each direction horizontally are equal in size, so there is no resultant force in this direction.

Resultant force = 5 N – 5 N = 0 N

RESULTANT FORCES – QUESTION 2

The vertical forces are not balanced, the bird will accelerate in a downwards direction.Resultant force = 5 N – 0

N = 5 N down

The vertical forces are equal in size and opposite in direction so there is no resultant force in the vertical direction. The horizontal forces are not balanced, so the yacht will accelerate to the right.

10 N

13 N

3. What is the resultant force on the yacht?

10 N

10 N

Resultant force = (20 N +10 N) – 13 N = 17 N right

RESULTANT FORCES – QUESTION 3

20 N

UPTHRUST QUIZ

FORCES – SUMMARY