P2.2 - Newton's Laws Flashcards
What can a force do?
Forces can change the shape of an object or change an object’s motion.
How can you represent forces?
- You cannot see a force.
- You can only see the effect of a force.
- You can represent forces as arrows in diagrams.
- Forces always have a size and a direction.
- Forces are measured in units of Newtons, N.
How can bodies interact to exert forces?
- By directly touching each other - Contact forces.
- At a distance, without touching - Non-contact
forces.
What is a field?
A field is a region where electrical/magnetic/mass bodies experience a force.
What happens when two bodies interact to produce a force?
- Each body exerts a separate force on the other.
- The two forces are the same in size, but in
opposite direction.
What is Newtons 3rd Law?
“When two bodies interact, they exert a force upon each other that is equal in size, but opposite in direction”
What is a free body diagram and what are they used to calculate?
- A free body diagram, is a diagram that shows all
the forces acting on a single body. - Free body diagrams are used to calculate the
resultant force that acts on a body.
What are the 3 steps to draw a free body diagram?
- Identify all the non-contact pairs.
2.Identify all the contact pairs. - Focus on a single object and draw that object
with arrows showing all the forces acting on
that object.
How do you calculate a resultant force when forces act in the same plane?
By adding and subtracting the forces.
How do you calculate a resultant force when forces act at 90 degrees to each other?
- Draw a force triangle from head to tail.
- The resultant force is the hypotenuse which can
be calculated either through calculation or by a
scale drawing.
What does it mean to resolve a force and how do you resolve a force?
- To resolve a force means to work out how much
of it acts in the horizontal plane and how much of
it acts in the vertical plane. - Make a triangle where the force is the
hypotenuse and the components are the sides. - Use a scale diagram or trig to calculate the
components.
How can you tell if and object is in equilibrium from their vectors?
When the forces acting on an object are in equilibrium, their vectors will form a closed shape when connected nose-to-tail.
What is Newton’s first law?
“A body will remain at rest, or continue to move at a uniform velocity, unless acted upon by a resultant force.”
What is inertia?
- Inertia is a measure of how difficult it is to
change the velocity of a body. - The greater the mass of a body, the greater its
inertia. - The more difficult it is to change its velocity the
more difficult it is to accelerate the body.
What is equilibrium?
- A body that does not accelerate (whether its at
rest or moving at uniform speed), is said to be in
a state of equilibrium. - In equilibrium, the resultant force acting on a
body is zero (in every plane)
What is Newton’s second law?
“The acceleration experienced by a body is directly proportional to the resultant force acting upon it, and in the same direction as. And, the acceleration is inversely proportional to mass.”
What can a resultant force do to an object?
- Change the speed of an object.
- Change the direction of motion of an object.
- Change both the speed and direction of motion of
an object.
What does Newton’s second law depend on?
- The size of the resultant force.
- The mass (inertia) of the object.
What equation do you need to apply in relation to Newton’s second law?
Force(N) = Mass (kg) x Acceleration
Why is a body moving in a circle at constant speed still accelerating?
- Constantly changing direction.
- Constantly changing velocity.
- Thus, constantly accelerating - Therefore must
be subject to a resultant force (centripetal force). - Centripetal force acts towards the centre of the
circle and acts only to change the direction of a
body the velocity (not the size).
Draw the components of the forces acting on a person on a slope.
What are the two planes we consider of an object on a slope?
- Plane parallel to the slope - The plane in which
the box tries to accelerate. - Plane perpendicular to the slope - The plane
in which the normal reaction force acts.
What is terminal velocity?
The velocity at which a body falls through a medium, when the drag acting on the body is equal to its weight.
The classic terminal velocity question:)
When the parachutist jumps, the drag force acting is small so the parachutist experiences a large acceleration due to the force of his weight.
As his speed increases, the drag force acting on him will increase, so the resultant force will decrease and his acceleration will decrease.
Eventually, the drag force will balance the weight. Acceleration is now zero and the speed is constant. The parachutist reaches a terminal velocity.
When the parachutist opens his parachute, the drag force will suddenly become very large, as the parachutist has a large surface area. This will cause Felix to start to decelerate.
As Felix is now slowing down, the drag force will start to decrease again until it balances his weight. Felix has now reached a new terminal velocity.
What is the equation of momentum?
p = m x v
Explain the Law of Conservation of Momentum.
- Momentum of a system (group of bodies
interacting) is always conserved. - The total momentum before an event is equal to
the total momentum after the event.
What is the difference between an elastic collision and an inelastic collision?
- Elastic collision - No energy transferred to other
stores. - Inelastic collision - Energy transferred to other
stores like sound to a thermal store
What are the two specific type of interactions?
- Bodies colliding and moving off together -
Stationary body with zero momentum is hit and
both bodies move off together. - Two stationary bodies, pushing off and moving
away from each other - Recoil and explosions -
Two bodies initially at rest end up moving away
from each other (sometimes in the same plane of
direction).
How do you calculate the force exerted in relation to momentum?
Force (N) = Change In Momentum (kgm/s) / Time (s)
What is work done and what are the units of work done?
- Work done is the transfer of energy between
stores. - Work is measured in units of Joules, J.
What is the equation for work done?
Work done (J) = Force (N) x Distance (m)
What does friction do?
Friction always transfers kinetic energy out of a body and transfers to heat whilst the force applied does work to transfer energy into the body.
What is power?
Power is the rate of energy transfer.
What is the equation for power?
Power (W) = Work done (J) / Time (s)
