Calculating the Force of Gravity

AIM: What are Newton’s three laws, and how do they describe how an object behaves?Do Now:- Draw a Free Body Diagram for the block below if1. it is at rest.2. If it is moving to the right at a constant velocity.3. If it is accelerating to the left.

Calculating the Force of Gravity • The force of gravity acting on an object is also known as the objects weight • weight is not mass! • Mass NEVER changes • The force of gravity (Fg) in Newtons, acting on an object depends on • the objects mass (m) in kilograms • the acceleration due to gravity (g) in m/s2 (changes if you are not on Earth) • The formula is Fg = mg

The Newton • The Newton is the unit of any force. • It is a derived unit, which means it is a combination of other fundamental units. • To determine the fundamental units a Newton is made up of • Find a formula for force • Plug in the unit for each variable • Combine the units

Calculating Weight • What is the weight of a 60Kg physics student? • A car weighs 20,000N. What is the car’s mass?

Newton’s 3 laws • 1st law: The Law of Inertia • An object at rest will stay at rest, and an object in constant velocity motion will stay in constant velocity motion unless acted on by a net (unbalanced) force. • INERTIA is an object’s “want” to resist a change in motion • INERTIA depends ONLY on the objects mass • The more massive, the more inertia regardless of the speed of the object. • 2nd Law: The law of acceleration • Fnet= ma • Ex: what is the acceleration of a 3kg mass being acted on by a unbalanced force of 6N? • 3rd Law:The law of action-reaction forces • ANY force acting on an object, has an equal and opposite reaction force • Force of “A” on “B” is equal and opposite to the force of “B” on “A”

Newton’s 1st law- objects in equilibrium • When an object is in equilibrium, the sum of all the forces acting on the object is zero. • We can make this statement more specific by saying • The sum of all the y-components of the forces are equal to zero • The sum of all the x-components of the forces are equal to zero.

1st law: The Law of Inertia Using Newton’s first law, explain why the table settings do not go flying

Newton’s 2nd LawFnet=ma • When solving force problems, ALWAYS follow these steps Step 1:find the motion statement in the problem. AT REST or CONSTANT VELOCITY or ACCELERATING Step 2: draw a Free Body Diagram of the object Step 3: Make a force statement based on your free body diagram and motion statement. IN EQUILIBRIUM – opposite forces are equal ACCELERATING – the vector sum of the forces =ma Step 4: solve

1. A 10kg crate is at rest on a horizontal surface. What is the Normal force acting on the crate? • Determine the object’s state of motion (Is it in equilibrium or not?) • Draw a free body diagram • Make a force statement based on the object’s state of motion • Solve for the missing forces

2. A 5kg crate is moving at a constant velocity on a horizontal surface while being pulled by a 20N force. A. What is the Normal force acting on the crate? B. What is the friction force acting on the crate? • Determine the object’s state of motion (Is it in equilibrium or not?) • Draw a free body diagram • Make a force statement based on the object’s state of motion • Solve for the missing forces

3. A 30kg crate is accelerating to the right at a rate of 2m/s2 while being pulled by a 40N force. A. What is the Normal force acting on the crate? B. What is the friction force acting on the crate? • Determine the object’s state of motion (Is it in equilibrium or not?) • Draw a free body diagram • Make a force statement based on the object’s state of motion • Solve for the missing forces

Hanging Signs and Tension in a string • Draw a Free Body Diagram for all the signs seen below. 40o 40o mA=5kg mB=5kg mC=5kg

Finding the Tension Force • Draw a free body diagram • Break down any angled forces if necessary. • Examine all the x-components and set their sum equal to zero 4. Examine all the y-components and set their sum equal to zero 5. Resolve your resultant vector A=5kg

Finding the Tension Force • Draw a free body diagram • Break down any angled forces if necessary. • Examine all the x-components and set their sum equal to zero 4. Examine all the y-components and set their sum equal to zero 5. Resolve your resultant vector 40o 40o mC=5kg

A 2000kg car is moving at a constant speed down a high way. If the engine provides a force of 300N, • what is the frictional force acting on the car? • What is the normal force acting on the car? • 2. A 6N force to the right acts concurrently with a 12N force to the left on a 3kg object. • What is the magnitude and direction of the net force acting on the object? • What is the magnitude and direction of the object’s acceleration? • What is the normal force acting on the object?

3. A 2Kg crate is accelerating to the right at 4m/s2 when acted on by a 14N force. • What is the friction force acting on the object? • What is the normal force acting on the object? • 4. A 30Kg child sits on top of a 10kg crate • What is the normal force acting on the child? • What is the normal force acting on the crate • 5. A 23Kg girl is sitting at rest in a tire swing. What is the tension in the rope?

A 30Kg child decides to ride in an elevator while standing on a scale that can read her weight. • What does the scale read while the elevator is at rest on the bottom floor? • What does the scale read as the elevator accelerates upward at 2m/s2 • What does the scale read as she moves upwards at a constant speed? • What does the scale read as she slows down at a rate of 1.5m/s2 when reaching the top floor? • What does the scale read as she accelerates downward at 3m/s2 on her way back to the loby? • What does the scale read as she moved downwards at a constant speed? • What does the scale read as she slows down at a rate of 2.5m/s2 when returning back to the ground floor?

Two children are fighting over a 2kg toy. If one child pulls to the right with a force of 20N and the other child pulls to the left with a force of 14N, what is the acceleration of the toy? • While pulling a 30Kg sled across the ice, one person uses a 40N force to the North while the other person uses a 60N force to the East? What is the magnitude of the resultant force?

9. A worker pushes a 20Kg crate across a horizontal surface at a constant speed. If the force the worker applies is 55N and an angel of 60o to the horizontal. • What is the vertical component of the push force? • What is the horizontal component of the push force? • What is the magnitude of the friction acting on the crate? • What is the normal force acting on the crate?

10. A mother pulls her 20Kg child in a wagon at a constant speed by applying a 100N force at an angle of 55o above the horizontal. • What is the vertical component of the pull force? • What is the horizontal component of the pull force? • What is the magnitude of the friction acting on the wagon? • What is the normal force acting on the wagon?

11. A 7Kg sign is hung from a horizontal ceiling with two ropes. One rope makes a 45o angle with the ceiling and the other makes a 60o angle. What is the tension in each rope? • 12. A 3kg sign is hung from a building with two chains. One chain is perfectly horizontal and attached to a side wall. The other chain makes a 25o angle to the vertical. What is the tension in each chain?

13. The following picture is hanging on a wall. • determine the weight of the picture.

14. The following sign can be found in Glenview. The sign has a mass of 50 kg. Determine the tension in the cables.

15. After its most recent delivery, the infamous stork announces the good news. If the sign has a mass of 10 kg, then what is the tensional force in each cable?

16. Find T1 and T2 T1 40o T2 12kg

17. Find T1 , T2 and T3 T1 40o T2 12kg T3 5kg

Calculating the Force of Gravity