1. Forces + Motion Flashcards
A vector quantity has
Magnitude and direction
A scalar quantity has
Only magnitude
Some examples of scalar quantities are
Distance speed time energy
Some examples of vector quantities are
Velocity Acceleration force displacement
Forces can change the
Speed shape and direction of something
Forces are measured in
Newton’s
What is the opposing force to motion
Friction
Air resistance is a form of
Friction
What is Newton’s first law
An object has a constant velocity unless acted upon by a resultant force
What is Newton’s second law
Force = mass x acceleration
What is Newton’s third law
Every action force has an equal and opposite reaction force.
What is mass
A measure of the amount of matter in an object
What is the formula for weight
W = mass x grav field strength
What is the grav field strength on Earth
10N/kg
Where does the weight of an object act from
It’s centre of gravity
What is speed
The distance travelled in a certain time
What is the formula for speed
S = distance / time
What is velocity
The speed in a given direction
What is acceleration
The change in velocity per unit time
What is the formula for acceleration
Change on velocity / time taken
In a distance time graph:
The gradient is
Velocity
In a distance time graph:
A negative gradient shows
It is returning back to the starting point
In a distance time graph:
A curved line means
It is accelerating
how can you measure friction
Measure the force used to overcome it
The more force needed the more friction
What affects friction
Surface
Mass
Gradient of the slope
Texture (Is the ramp straight + smooth?)
Which has more friction, an object of the same shape and size on a shallower or steeper slope?
A shallower slope because there is more friction to overcome it (more force more friction)
Why is friction good?
Necessary for some things to move like walking
Starts chemical reactions like fire
Allows break for cars
Why is friction bad?
Slows things down
Damages, wears down moving parts
Heats up moving parts
How to reduce friction
Lubricate surfaces (grease, oil, water) Use ball bearings Make surfaces smooth Reduce surface area in contact Reduce the force pushing them together because the less force the less friction
What does SUVAT stand for
S - displacement (distance) U - initial speed V - final speed A - acceleration T - time
Which property of a velocity-time graph can be used
to calculate distance travelled?
Area under the graph
State an equation linking final speed, initial speed,
acceleration and distance travelled
v² = u² + 2as
Name two types of forces that always
opposes motion
- Friction
2. Air Resistance (Drag)
a) Which type of force holds planets around the Sun?
b) Which type of force holds electrons around the nucleus?
a) Gravitational Force
b) Electrostatic Force
State the ways that a force can affect the body that it
is being applied on
-It can change the shape of the object
(extension/compression)
-It can change the speed of the object
-It can change the direction the object is moving
State an equation linking unbalanced force, mass
and acceleration
Force (N) = Mass(kg) x Acceleration (m / s^2)
F = m x a
State an equation linking mass, weight and
gravitational acceleration
Weight(N) = Mass(kg) x g (m / s^2) W = mg
What is the relationship between stopping
distance, braking distance and thinking distance
of a car while stopping?
Stopping Dist. = Thinking Dist. + Braking Dist.
State 3 factors that affect the stopping distance of a
car
- Reaction time
- Weather conditions
- Initial speed
- Driver’s conditions
- Road Conditions
- Mass of the car
- Tire Conditions
State two factors that affect the air
resistance acting on a falling object
- Surface Area
- Speed
Describe how a falling object reaches terminal
velocity
At first the object falls under the effect of its weight accelerating with g. As it accelerates, air resistance opposing the motion increases therefore the resultant force acting on the object decreases and since F=ma, acceleration decreases. When air resistance becomes equal to weight, forces are balanced so the resultant force=0 therefore a=0 and object reaches terminal velocity.
State what is meant by obeying Hooke’s Law
Extension is directly proportional with the
force applied.
Explain what is the difference between elastic and
plastic behavior.
- In elastic behaviour, object recovers its original shape when the forces causing the extension is removed.
- In plastic behavior, there is a permanent deformation to the shape of the object when forces are removed.
What is momentum
The product of an object’s mass and velocity
What is the equation for momentum
Momentum = mass × velocity p = m × v
What are the units for momentum
Kilogram metres per second (kgm/s)
Change in momentum over time is equal to what
The force exerted on an object
Force (momentum) equation
Force = change in momentum/time F = mv-mu/t
What is the principle of the conservation of momentum
The total momentum before is equal to the total momentum after
What is the equation for Hooke’s law
𝐹 = 𝑘𝑥 where F is the force applied to the spring, k is the
spring constant, and x is the extension.
What does a linear force/extension (straight line) graph show
Elastic deformation following Hooke’s law
- The point it stops being linear is called the
limit of proportionality. From then on, it
does not obey Hooke’s law.
- Gradient is the spring constant, k
What does a non-linear (curved line) force-extension graph show
Deformation not following Hooke’s law
• After this region, it will fracture
What is a moment
A measure of something’s turning effect measured in newton metres
How do you work out the moment
Moment = force x perpendicular distance from pivot point
What is the principle of moments
Sum of clockwise moments = sum of Anti-clockwise moments also there is no resultant force
What affect does a resultant force have on an object moving at a steady speed
It makes it accelerate which can either be positive or negative (decelerate). Which makes it speed up, slow down change direction
How do you work out the gradient
y2-y1/ x2-x1
What is a turning force
A force which rotates either clockwise or anti-clockwise
What is a pivot/fulcrum
Is a point about which an object can be turned or rotated
How would you balance a big person and a small person on a seesaw so it’s balanced
The smaller person goes further away form the pivot and the bigger person goes closer
