basketball; Newton's laws of motion When a basketball player shoots a jump shot, the ball always follows an arcing path. The ball follows this path because its motion obeys Sir Isaac Newton's laws of motion. Newton’s laws first appeared in his masterpiece, Philosophiae Naturalis Principia Mathematica (1687), commonly known as the Principia. In 1543 Nicolaus Copernicus suggested that the Sun, rather than Earth, might be at the centre of the universe. In the intervening years Galileo, Johannes Kepler, and Descartes laid the foundations of a new science that would both replace the Aristotelian worldview, inherited from the ancient Greeks, and explain the workings of a heliocentric universe. In the Principia Newton created that new science. He developed his three laws in order to explain why the orbits of the planets are ellipses rather than circles, at which he succeeded, but it turned out that he explained much more. The series of events from Copernicus to Newton is known collectively as the Scientific Revolution.

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12. 1. If a bike with a rider having a total mass of 63 kg brakes and reduces its velocity from 8.5 m/s to 0 m/s
in 3.0 second. What is the magnitude of the braking force?
The combined mass of the bike and the rider is 63 kg The initial velocity of the bike is m = 8.5 m/s
The final velocity is 0
The time in which the bike stops is Δt = 3.0 s
The net force acting on the body is equal to the rate of change of momentum of the object.
F=ΔpΔt
The momentum of a body with mass m and velocity v is given by p = mv
Hence, the change in momentum of the car is given by
Δp=mv−mu=m(v−u)
Hence, the net force acting on the car is given by F=m(v−u)Δt
Substituting the value, we get F=63kg×(0−8.5m/s)3.0s F=1.8×102N

13. 2. Calculate the net force required to give an automobile of mass 1600 kg an acceleration of 4.5 m/s2
We calculate the force as follows: F = ma
Substituting the values in the equation,
we get F = 1600 kg × 4.5 m/s2
F = 7200 N
The net force required to the automobile an
acceleration of 4.5 m/s2.

14. 1) While driving to work, Naveen always keeps his purse on the passenger seat. By the time he gets to
work, his purse would have fallen on the floor in front of the passenger seat. One day, he asks you to
explain why this happens in terms of physics. What do you say?
We can explain this to Naveen in terms of Newton’s first law
of motion. The purse due to inertia travels forward with the
car until acted upon by another force, in this case, the force
of the car floor.

15. 2) Which of Newton’s laws best explains how a magician can pull a
tablecloth from underneath dishes?
Newton’s first law of motion can explain how a magician pulls a
tablecloth from underneath the dishes. A negligible horizontal force is
applied during the process. As per Newton’s first law of motion, the
dishes and glasses remain in their state of motion (rest), as a result,
they remain undisturbed. The table cloth in the trick is made so
slippery such that it doesn’t apply any frictional force on glasses and
dishes.

17. Q1: What is the SI unit of Force
Ans: SI unit of Force is newton
Q2: State the relationship between force, mass, and acceleration.
Ans: The relationship between force, mass, and acceleration are given by the formula F=ma.
Q3: If the mass of the body increases, keeping the acceleration constant, what happens to the net force?
Ans: If the mass of the body increases keeping the acceleration constant the net force increases.
Q4: For a constant mass. If acceleration decreases, what happens to net force?
Ans: For a constant mass. If acceleration decreases, the net force also decreases.
Q5: If the rate of change of momentum is small, what will be the net resultant force?
Ans: If the rate of change of momentum is small, the net resultant force will also be small.
Q6: If Mr. John wants to move a 10 kg and 20 kg solid block from the rest, which block needs more force?
Ans: If Mr. John wants to move a 10 kg and 20 kg solid block from the rest block with 20 kg, he needs a higher force.
Q7: Newton’s first law of motion is alternatively called as _________.
Ans: Newton’s first law of motion is alternatively called a law of inertia.
Frequently Asked Questions – FAQ’s

18. Apparent Weight of a Body in a Lift

31. • Friction is a force between two surfaces that are sliding, or
trying to slide across one another, for example when you try to
push a toy car along the floor.
• Friction always works in the direction opposite from
the direction the object is moving, or trying to move. It
always slows a moving object down.
Moving
Friction

32. • The amount of friction depends on the materials from which the two
surfaces are made. The rougher the surface, the more friction is produced. For
example, you would have to push a book harder to get it moving on a carpet
than you would on a wooden floor. This is because there is more friction
between the carpet and the book than there is between the wood and the book.

33. • Friction also produces heat. For example, if you rub
your hands together quickly, they get warmer.

34. • Friction can be a useful force because it prevents our shoes
slipping on the pavement when we walk and stops car tyres
skidding on the road.

35. • Ice causes very little friction, which is why it is easy to slip
over on an icy day. But this is a good thing for ice skating and
sledging.

36. • Sometimes we want to reduce friction. For example, moving
parts inside a car engine are lubricated with oil, to reduce friction
between them. The oil holds the surfaces apart, and can flow
between them. The reduced friction means there is less wear on
the metal, and less heat produced.

37. • Air resistance is a type of friction between air and another
material. When an aeroplane flies through the air, for
example, air particles hit the aeroplane, making it more
difficult for the aeroplane to move through the air.

38. • Some shapes, known as streamlined shapes, cause less
air resistance than others. Aeroplanes and cars are
streamlined, so that they move through the air as easily
as possible.

39. Friction Factors Review
1. Roughness – The rougher the surface, the more
hills and valleys there are and the greater the friction.
2. Force pushing together/weight – Force is
increased, the hills and valleys will be in closer
contact and friction will increase.

40. Amount of Surface Area in fluids
• The amount of surface area affects the friction
between objects in liquids and gases. Example:
Swimming

41. Surface Area in Fluids
• The amount of surface area affects the friction on
a moving object under the following circumstances:
– air resistance (such as the size of a parachute)
– the resistance of an object as it glides through water
(such as a boat).

42. Surface area between Solids
• The amount of surface area in
contact usually does not
affect friction between two
solids.
- Reason larger surface areas
have more contact but the
pressure between the 2 is less.
The increase in friction area is
offset by the reduction in
pressure

43. Types of Friction
1. Sliding
2. Fluid
3. Rolling
4. Static

44. Sliding Friction
• Sliding friction is a friction
force that opposes the
direction of motion of an
object that occurs when solid
surfaces slide over one
another.
• Examples:
– Writing – pencil point and
paper
– Combing your hair – surface of
comb and strands of hair

45. Fluid Friction
• The force that tries to slow objects down
when they move through a liquid or a gas.
It's also known as "drag", or "air resistance".
• All gases and liquids are fluids.
• Fluid Friction increases as the speed of the
object increases.
• An airplane and a swimmer both experience
fluid friction.

46. Rolling Friction
• Rolling friction is
friction that occurs
between surfaces in
motion that are rolling in
which one of the
surfaces is a wheel,
roller, or ball.
• Examples:
– Riding a bike – tires and
ground
– Bowling – ball and lane

47. Static Friction
• Static friction is friction
that occurs when the
surfaces in contact are
at rest (not in motion).
• Examples:
– A book resting on a desk.
– A potted plant sitting on a
sidewalk.

48. Ways to Reduce Friction
• Smooth the surface – less hills and valleys and there are
not as deep.
• Replace sliding with rolling (Use Wheels)
• Add a lubricant like oil, wax, or grease – Fills in the hills
and valleys.
• Less force pushing together – The hills and valleys are
not pushed together as hard so they have less contact.

49. Ways to Increase Friction
• Rough the surface – more hills and valleys and there are
not are deeper.
• Replace rolling with sliding
• More force pushing together – The hills and valleys are
pushed together harder so the hills and valleys are in
closer contact.

50. Glass
Forces: Friction
Turn to a partner and identify surfaces
that may cause more friction.
Sandpaper
Carpet
Gravel
Less Friction?ICE
Tile

51. Forces: Friction
Friction is both harmful and helpful.
Turn to an elbow partner and identify
some examples of friction being harmful
and friction being helpful.

52. Forces: Friction

53. Forces: Friction
Is it beneficial to
reduce or increase
friction? Why or
Why Not?

54. Forces: Friction
Which of the following would NOT help
you move a heavy object across a
concrete floor?
Water, ball bearings, oil, liquid soap,
steel rods, foam rubber
Name three common items you might
use to increase friction.