Transcript forces

UNIT 2
FORCES IN ACTION
MACHINES MOVE THE WORLD
L3 L4 L5
L6
Marta Vidal Vidal
ISAAC NEWTON (1642-1727)
FIRST LAW OF MOTION. INERTIA
An object at rest stays at rest,
an object in motion stays in motion.
Why does an object stop its motion?
Why do objects change its direction?
Because it is the result of an
UNBALANCED FORCE
applied upon an object.
Unbalanced force
Start motion
Stop motion
Change direction
Change shape
Balanced force
• No change
• No visible effect
WHICH FORCES INFLUENCE MOTION?
Contact forces
FORCE is any influence that causes
Friction
a free body to undergo a change in
Push/Pull
speed, a change in direction, or a
change in shape.
Weight
Non-contact forces
Gravity
Magnetism superconducting
HANDS ON! Friction
PROBLEM:
How do different surfaces affect the movement of the objects?
MATERIALS:
Pencil, toy car, metric tape, 4 clothespegs, tape, scissors, aluminium foil, wax
paper, recycled paper, sand paper, a calculator and plastic cable covers.
STEPS:
1. Predict the distance of the toy car on each surface.
2. Create a ramp using 4 clothespegs and plastic cable covers.
3. Drop the toy car and measure the distance.
4. Do 3 different trials for each surface and calculate total distance.
Play with friction
HANDS ON! Friction
PROBLEM:
How do different surfaces affect the movement of the objects?
STEPS:
1. Predict the distance of the toy car on each surface.
SURFACE
PREDICTION
cm
TRIAL 1
cm
TRIAL 2
cm
TRIAL 3
cm
DISTANCE
T1+T2+T3
3
Aluminium
foil
cm
Wax paper
cm
Recycled
paper
cm
Sand paper
cm
HANDS ON! Friction
PROBLEM:
How do different surfaces affect the movement of the objects?
STEPS:
2. Create a ramp using 4 clothespegs and plastic cable covers.
HANDS ON! Friction
PROBLEM:
How do different surfaces affect the movement of the objects?
STEPS:
3. Drop the toy car and measure the distance.
4. Do 3 different trials for each surface and calculate the total
distance.
Total distance = trial 1 + trial 2 + trial 3
3
SURFACE
PREDICTION
cm
TRIAL 1
cm
TRIAL 2
cm
TRIAL 3
cm
DISTANCE
T1+T2+T3
3
Aluminium
foil
cm
Wax paper
cm
Recycled
paper
cm
Sand paper
cm
WEIGHT
ENGLISH DECIMALS IS IN . (DOT)
SPANISH DECIMALS IS IN , (COMMA)
MASS is a measurement of how much matter is in an
object.
WEIGHT is a measurement of how hard gravity is
pulling on that object.
On Earth 1 kg of mass = 9.8 newtons
Gravity on Earth is 1G = 9.8 newtons
WEIGHT = MASS x GRAVITY
WEIGHT = 1kg x 1 1
WEIGHT = 1 Kg or is = 9.8 newtons
On Earth our mass is equal to our weight.
MASS = 1kg WEIGHT= 1kg
Our
MASS
is the same
if
What
will happen
to everywhere
our weightbut
if we
we travel over the universe we have a
travel
around
space?
different WEIGHT
MASS = 60 Kg
WEIGHT = 60 Kg
MASS = 60 Kg
WEIGHT = 60 x 0.16
WEIGHT = 9.6 Kg
Calculate your weight in the Solar System
Look at the gravity of the planets, the sun and the Moon and
calculate your weight in respect to those.
Sun
27,90
Mercury
0,37
Venus
0,88
Earth
1,00
Mars
0,38
Jupiter
2,64
Saturn
1,15
Uranus
0,16
Neptune
1,22
Moon
0,16
your
MASS
your
WEIGHT
IS EQUAL TO
GRAVITY
MULTIPLIED BY
Planets, Star and
satellite
Look at your results and underline the correct part of the sentence.
Is it your weight different or is it equal?
My weight
never changes.
changes.
Is it your mass different or is it equal?
My mass never changes.
changes.
Calculate your weight in newtons
On Earth
On the moon
Weight = mass x gravity in newtons
WEIGHT = ………. x 9,8
WEIGHT = ………. x 1,5
WEIGHT = ….....newtons WEIGHT = ….....newtons
WHAT IS FORCE?
It can be a PUSH or a PULL.
OBJECT
PUSH
FORCE
PULL
FORCE
Is it a push or a pull?
ISAAC NEWTON (1642-1727)
SECOND LAW OF MOTION.
THE UNIT FOR THE FORCE IS IN NEWTONS
The strength of a force is equal to the amount of the mass
involved multiplied by any acceleration applied to it.
F=mxa
If the mass is bigger the effect of the FORCE is smaller
F
If the mass is smaller the effect of the FORCE is bigger
F
HANDS ON! Newtons
MATERIALS:
- Pencil
- Tape measure
- Weighing scale
- Dynamometer
- 3 objects.
PROBLEM:
How do you use a dynamometer?
What is the relationship between mass and force?
STEPS:
1. Predict the power of the force needed to move the objects. Write a number
from 1 to 3 (from bigger force to a smaller force).
Objects
PREDICTION
MASS
FORCE
NEWTONS
Result
HANDS ON! Newtons
MATERIALS:
- Pencil
- Tape measure
- Weighing scale
- Dynamometer
- 3 objects.
PROBLEM:
How do you use a dynamometer?
What is the relationship between mass and force?
STEPS:
2. Measure the objects with a weighing scale and record it in your data table.
Objects
PREDICTION
MASS
FORCE
NEWTONS
Result
HANDS ON! Newtons
MATERIALS:
- Pencil
- Tape measure
- Weighing scale
- Dynamometer
- 3 objects.
PROBLEM:
How do you use a dynamometer/spring scale?
What is the relationship between mass and force?
STEPS:
3. Put a tape measure on the floor and measure 100 cm in straight line.
4. Attach the object to the dynamometer and pull it along a distance of
100 cm and record the result in your data table.
Objects
PREDICTION
MASS
FORCE
NEWTONS
Result
HANDS ON! Newtons
MATERIALS:
- Pencil
- Tape measure
- Weighing scale
- Dynamometer
- 3 objects.
PROBLEM:
How do you use a dynamometer?
What is the relationship between mass and force?
STEPS:
5. Write your conclusion about the experiment.
6. Share and check the results with the whole class.
Write your CONCLUSIONS
If the mass of an object is
bigger
smaller
the force needed to move it is
bigger
smaller.
If the mass of an object is bigger the force needed to move it is bigger.
If the mass of an object is smaller the force needed to move it is smaller.
ISAAC NEWTON (1642-1727)
THIRD LAW OF MOTION
ACTION AND REACTION
All forces occur in pairs.
For every action that takes place there
is an equal and opposite reaction.
FORCE
CONTACT
FORCES
It is any influence that causes a free body to
undergo a change in speed, a change in
direction, or a change in shape.
It is a force that acts at the point of contact
between two objects.
FRICTION
It is the force resisting the relative motion of
solid surfaces, fluid layers, and/or material
elements sliding against each other.
PULL
It is a force that can move something
towards somebody/something.
PUSH
It is a force that can move something away
from somebody/something.
NON-CONTACT
FORCES
It is a force applied to an object by another
body that is not in direct contact with it.
MAGNETISM
Force of attraction or repulsion acting
between ferromagnetic materials like iron.
GRAVITY
It is a force that pulls all objects towards the
center of the Earth.