Unit 5 : Forces -

Question: What is force
Answer: Force is a push or pull acting on an object

Question: What are types of forces
Answer: Contact forces and non contact forces

Question: What are contact forces
Answer: They act when objects touch

Question: What are non-contact forces
Answer: They act from a distance

FORCE DIAGRAM

Question: What are force diagrams
Answer: Force diagrams show the forces acting on an object

Question: What do force diagrams use to show forces
Answer: They use arrows

Question: What does the arrow direction show
Answer: It shows the direction in which the force is acting

Question: What does the arrow length show
Answer: It shows the strength of the force
Longer arrow means stronger force

Question: What does the base of the arrow show
Answer: It shows the point from where the force is acting

Question: What must be written on a force diagram
Answer: The name of the force and the two objects involved

MOTION

Question: How do forces affect motion
Answer: Forces can change the way an object moves

Question: What is motion
Answer: Motion is the way an object moves

Question: What are balanced forces
Answer: Balanced forces have equal strength but act in opposite directions

Question: What effect do balanced forces have on motion
Answer: Balanced forces do not change the motion of the object

Question: Can an object still be moving if forces are balanced
Answer: Yes, an object can still be moving even when forces are balanced

Question: What happens if an object is moving with balanced forces on it
Answer: It keeps moving at the same speed and in the same direction

Question: What happens if an object is still with balanced forces on it
Answer: It stays still

BALANCED FORCES

There are two forces acting on the panda :
Weight due to Earth pulling it down.
Support force from the table pushing it up.

a. The panda is an example of balanced forces. How do you know?
The panda is not moving. The weight pulling it down and the support force from the table pushing it up are equal, so the forces are balanced.

b. Who do you think has the correct scientific answer?
The girl who says there are two forces acting on the panda has the correct answer.

c. Why do you think the other answers are incorrect?
The boy who says only weight acts is wrong because the table also pushes up.
The boy who says no forces act is wrong because weight always acts.
The girl who says a table cannot push is wrong because the table gives a support force.

d. What would you do to convince others about the correct answer?
I would explain that if the table did not push up, the panda would fall. The panda stays still because the upward support force balances the downward weight.

Question: What happens when forces on an object are balanced
Answer: The object will stay still or keep moving at the same speed

Question: What is steady speed
Answer: It is when an object is moving and its speed does not change

Question: What does unbalanced force mean
Answer: One force is stronger than the force in the opposite direction

Question: What do unbalanced forces do
Answer: They change the motion of the object

Question: What happens when forces on an object are unbalanced
Answer: The motion of the object will always change

Question: How can the motion change when forces are unbalanced
Answer: The object can speed up or slow down

MASS & WEIGHT

Question: What is mass
Answer: Mass is the amount of matter in an object. It is measured in kilograms or grams.

Question: What is weight
Answer: Weight is the force that pulls an object downward due to gravity.

Question: What causes weight
Answer: Weight happens when two masses attract each other through gravity.

Question: Why are mass and weight different
Answer: Mass is the amount of matter. Weight is the pull of gravity on that mass.

Question: What type of force is weight
Answer: Weight is a non contact force because gravity acts from a distance.

Question: What is the unit of weight
Answer: Weight is measured in newtons.

Question: What is gravitational attraction
Answer: It is the pull between masses everywhere in the universe.

Question: What creates the weight of an object
Answer: The pull between the mass of Earth and the object creates weight.

Question: What is the unit of gravitational attraction
Answer: It is measured in newtons per kilogram.

Question: How much does one kilogram of mass weigh on Earth
Answer: It weighs about ten newtons.

Question: Does this value stay the same everywhere in the universe
Answer: No. It is only true on Earth.

Question: An astronaut has a mass of sixty kilograms. What is her weight on Earth
Answer: Her weight is about six hundred newtons.

Question: How strong is the Moon’s gravitational attraction compared to Earth
Answer: It is about one sixth of Earth’s attraction.

Question: What is the astronaut’s weight on the Moon
Answer: Her weight is about one hundred newtons.

Question: Does her mass change on the Moon
Answer: No. Her mass stays sixty kilograms.

Weight on Earth is about ten newtons for each kilogram.
Weight on the Moon is about one sixth of the Earth weight.

a. Skateboard
Mass 3 kg
Weight on Earth about 30 N
Weight on Moon about 5 N

b. Bag of rice
Mass 2.4 kg
Weight on Earth about 24 N
Weight on Moon about 4 N

c. Book case
Mass 66 kg
Weight on Earth about 660 N
Weight on Moon about 110 N

d. Bowling ball
Mass 7.2 kg
Weight on Earth about 72 N
Weight on Moon about 12 N

e. Travel bag
Mass 12 kg
Weight on Earth about 120 N
Weight on Moon about 20 N

f. School chair
Mass 3.6 kg
Weight on Earth about 36 N
Weight on Moon about 6 N

Question: Does air have mass
Answer: Yes. Air and gases around us also have mass.

Question: What is the total mass of Earth’s atmosphere
Answer: It is about 5.7 quadrillion tons.

Question: What is this mass equal to in simple comparison
Answer: It is equal to about five hundred seventy trillion adult Indian elephants.

Question: What do we use air for in tyres
Answer: We use air to fill tyres so they work properly.

Question: What happens if a tyre is not inflated correctly
Answer: It can cause problems in driving and safety.

Question: Why are under inflated tyres a concern
Answer: They can create many driving and environmental problems.

Question: What do under inflated tyres increase
Answer: They increase fuel use.

Question: How do under inflated tyres affect pollution
Answer: They increase the carbon dioxide released by vehicles.

Question: How do under inflated tyres affect stopping distance
Answer: They increase the distance needed to stop.

Question: How do under inflated tyres affect steering
Answer: They make steering less precise.

Question: What risk increases with under inflated tyres
Answer: The risk of aquaplaning increases.

Question: How do under inflated tyres affect tyre wear
Answer: They cause more damage and make the tyre more likely to fail quickly.

a. The astronaut’s weight on the Moon is less than her weight on Earth. Why?
Answer: The Moon pulls with less force than Earth, so her weight is smaller on the Moon.

b. The astronaut’s mass on the Moon is the same as her mass on Earth. Why?
Answer: Her mass does not change because it is the amount of matter in her body, and that stays the same everywhere.

WEIGHT IN WATER

Question: What can masses do
Answer: Masses can apply a force on other objects.

Question: Can solids, liquids and gases apply a support force
Answer: Yes. They can all apply a support force on objects they touch or interact with.

Question: What happens when an object interacts with a liquid
Answer: The liquid applies a force on the object.

Question: When will an object float in a liquid
Answer: It will float if the liquid pushes back enough on the object.

Question: When will an object sink in a liquid
Answer: It will sink if the liquid cannot push back enough on the object.

UPWARD FORCE

Question: What is the force that pushes up on objects in water
Answer: The upward force is called upthrust.

Question: What happens to weight when the mass of an object increases
Answer: The weight increases.

Question: When does an object sink in water
Answer: It sinks when its weight is greater than the upthrust.

Question: Can the shape of an object change the upthrust
Answer: Yes. The shape can change how strong the upthrust is.

Question: How can upthrust be increased
Answer: By increasing the surface area of the object that is in the water.

Question: Why can metal boats with heavy cargo float
Answer: They float because their shape increases upthrust enough to balance their weight.